The official suffix -um- signals an unspecified relationship to the base. Unlike -ej- “place for,” -il- “instrument for,” or -id- “offspring of,” it supplies no single relationship that lets you calculate every word. Folio → foliumi means “leaf through pages,” brako → brakumi means “hug,” and malvarma → malvarmumi means “catch a cold.” Each must largely be learned as vocabulary.
This is not a flaw or a license to guess. The Fundamento explicitly presents -um- as having no defined meaning and tells learners to learn its few words individually. Modern Esperanto has expanded the set, but lexical convention and attested use still matter more here than with a narrowly defined affix.
What -um- does—and does not say
The structure is regular: base + -um- + grammatical ending. The meaning is only “something conventionally related to the base.”
| Base | Established word | Conventional meaning |
|---|---|---|
| folio | foliumi | leaf through a book or magazine |
| brako | brakumi | hug, put one's arms around |
| aero | aerumi | air or ventilate |
| mano | manumo | cuff of a sleeve |
The suffix does not mean “use,” “apply,” “become,” or “part of” in general. Those are recurring relationships found in particular groups, not alternative dictionary definitions of -um-.
Mi foliumis la revuon dum mi atendis la kuraciston.
I leafed through the magazine while I waited for the doctor.
La infano brakumis sian patron antaŭ ol eniri la lernejon.
The child hugged their father before entering the school.
Acting with a body part or related object
Several established verbs denote a characteristic action involving the base. Their exact actions are conventional:
- palpebrumi means blink, using the eyelids;
- brakumi means embrace with the arms;
- okulumi means give someone an interested or amorous look;
- foliumi means turn pages while browsing.
Ŝi palpebrumis pro la forta lumo, ne ĉar ŝi volis doni sekretan signon.
She blinked because of the bright light, not because she wanted to give a secret signal.
Ĉu vi jam legis la raporton? — Ne, mi nur rapide foliumis ĝin.
Have you read the report yet? — No, I only leafed through it quickly.
The short exchange shows why foliumi is not simply legi. It conventionally suggests turning through pages and reading only selectively. Likewise, okulumi is not the neutral verb “look”; rigardi is neutral, while okulumi carries a socially marked interested look and is usually (informal).
❌ Li okulumas sian amikon ĉe la alia tablo.
Nonconventional if the intended meaning is simply ‘He looks at his friend’: okulumi carries a marked interested or amorous sense.
✅ Li rigardas sian amikon ĉe la alia tablo.
He is looking at his friend at the other table.
The diagnostic pair shows that established okulumi does not merely mean neutral visual attention. Convention outranks the vague compositional possibility.
Applying or exposing something
Another cluster involves bringing the base substance or medium into contact with something:
- aerumi — expose to air or let air in to freshen;
- sunumi — expose oneself or something to sunshine;
- sukerumi — coat or sprinkle with sugar;
- sapumi — apply soap.
Bonvolu aerumi la ĉambron antaŭ ol la gastoj alvenos.
Please air the room before the guests arrive.
La bakisto sukerumis la varmajn kukojn.
The baker coated the warm cakes with sugar.
Ni ne sunumu tro longe sen protekto.
Let's not sunbathe or expose ourselves to the sun too long without protection.
These resemble ordinary denominal verbs such as akvi “apply water” and ori “coat with gold.” In fact, -um- may be unnecessary when a simple verb already has the clear conventional meaning. PMEG recommends butoni, akvi, and sali rather than automatically adding -um-.
Related objects, parts, and conditions
Some -um- nouns name an object or condition related to the base in a relationship that must be memorized:
- manumo — a cuff, the sleeve part at the wrist/hand;
- kolumo — a collar;
- malvarmumo — a cold, the illness;
- brulumo — an inflammation.
La manumoj de ĉi tiu ĉemizo estas tro streĉaj.
The cuffs of this shirt are too tight.
Mi ne venos hodiaŭ, ĉar mi malvarmumis kaj ankoraŭ tusas.
I won't come today because I caught a cold and am still coughing.
Malvarmumi does not mean simply “be cold” or “become colder.” Those meanings are malvarmi and malvarmiĝi according to context. The -um- verb is the lexicalized illness expression.
La supo malvarmiĝis, sed mi ne malvarmumis.
The soup became cold, but I did not catch a cold.
That minimal contrast makes the lexical boundary explicit.
Diverse established meanings
Other common words resist even a loose shared paraphrase:
Ni plenumis ĉiujn kondiĉojn de la kontrakto.
We fulfilled all the conditions of the contract.
Gustumu la saŭcon antaŭ ol aldoni pli da salo.
Taste the sauce before adding more salt.
Mi cerbumis dum horo, sed ankoraŭ ne trovis solvon.
I racked my brains for an hour but still did not find a solution.
Plenumi conventionally means carry out or fulfill a task, duty, wish, or condition—not generally “make full,” which is plenigi. Gustumi means sample or perceive a taste, not merely “have a taste,” and cerbumi means think hard. Their base offers a mnemonic, but not a complete definition.
Mathematical terminology supplies another established family: duuma “binary,” dekuma “decimal,” and deksesuma “hexadecimal.” These are (technical) terms in which -um- connects a number with the size of a numeral system.
Komputiloj interne uzas duuman nombrosistemon.
Computers internally use the binary numeral system.
How to read an unfamiliar -um- word
An unfamiliar -um- form gives you two pieces of reliable information: its base and its grammatical ending. In ŝtonumado, for example, ŝton- points toward stones, -ad- presents an ongoing or repeated activity, and -o makes the result a noun. What remains unspecified is the crucial relation between stones and the activity. It could be throwing stones, covering something with stone, or something else established in a particular community. Morphology narrows the search without completing it.
Use three levels of evidence. First, the immediate sentence may reveal participants and result. Second, a dictionary may record a conventional lexical meaning. Third, corpus examples show whether that meaning is current and what objects or complements normally accompany it. A single playful occurrence demonstrates that a writer could make the form understandable; it does not by itself make the word neutral vocabulary.
English speakers face the same issue in reverse with opaque verbs such as “to stone,” which can mean throw stones at someone rather than merely use stone in any manner. The difference is that Esperanto openly marks the relation as underspecified with -um-. That warning should make you more cautious, not more willing to invent a translation.
Ĉu vi konas la vorton ‘ŝtonumi’? — Jes, sed mi kontrolos la precizan sencon en vortaro.
Do you know the word ŝtonumi? — Yes, but I will check the precise meaning in a dictionary.
Why new -um- words are risky
Grammatically, speakers can create occasional -um- words, and context or humor may make them understandable. But the suffix deliberately withholds the relation. A new telefonumi could mean telephone someone, fiddle with a phone, spend time on a phone, or equip something with phones. Esperanto already has telefoni, so -um- adds uncertainty without need. The broader page on coining understandable new words explains when an improvised form is likely to succeed.
❌ Mi telefonumis al la hotelo por mendi ĉambron.
Nonconventional and needlessly unclear when the established verb telefoni expresses the action.
✅ Mi telefonis al la hotelo por mendi ĉambron.
I phoned the hotel to book a room.
The independent words umo “thingamajig” and umi “do something hard to name” occur (informal, playful). Their vagueness is the point, and they are inappropriate where precision matters.
Kion vi umas en la kuirejo? — Mi provas ripari la kafmaŝinon.
What are you fiddling with in the kitchen? — I'm trying to repair the coffee machine.
Status and evidence
-um- is Fundamenta and official. That status guarantees the suffix as part of Esperanto; it does not guarantee a meaning for every possible combination. PMEG's semantic clusters are descriptive aids, while dictionaries and corpus evidence establish whether an individual form is ordinary, rare, technical, or one-off.
For active use, learn frequent forms—plenumi, brakumi, foliumi, aerumi, gustumi, manumo, kolumo, and malvarmumi—as separate lexical items. When encountering an unfamiliar formation, context may suggest a meaning, but verify it rather than treating the guess as a rule.
Common Mistakes
1. Assigning one fixed translation to -um-.
❌ Brakumi signifas ‘uzi brakon por ajna ago’.
Incorrect: brakumi conventionally means ‘hug.’
✅ Ŝi brakumis sian amikon ĉe la stacidomo.
She hugged her friend at the station.
2. Using -um- whenever the relation is unknown.
❌ Mi librumis ĝin sur la tablon.
Incorrect and opaque: -um- cannot replace a relation the speaker has not expressed.
✅ Mi metis la libron sur la tablon.
I put the book on the table.
3. Treating a conventional word as freely compositional.
❌ Plenumi la botelon signifas plenigi ĝin per akvo.
Incorrect: plenumi means fulfill or carry out, not physically fill.
✅ Plenigu la botelon, sed plenumu la promeson.
Fill the bottle, but fulfill the promise.
Key Takeaways
- -um- marks an unspecified relation; each established word needs its own lexical meaning.
- Recurring clusters help memory but are not fixed productive rules.
- Simple derivation or a dedicated affix is preferable when it expresses the relationship clearly.
- New -um- coinages depend unusually heavily on context and attestation.
- Independent umo and umi are playful, vague forms rather than neutral technical vocabulary.
Related Topics
- Lexicalization and ConventionalityB2 — Understand why structurally transparent Esperanto words develop conventional meanings that cannot be predicted from morphology alone.
- Coining Understandable New WordsB2 — Create transparent Esperanto words by choosing a clear semantic head, explicit relation, economical structure, and a form that listeners can interpret without private guesswork.
- Affix Stacking and ScopeB2 — Interpret and build multi-affix Esperanto words by applying each layer in order and keeping the semantic head and participant roles clear.
- Conciseness versus Over-DerivationC1 — Choose between compact derived words and explicit phrases by preserving semantic scope, conventionality, and reader effort.
- Humor, Irony, and Playful Word FormationC1 — Create and interpret Esperanto humor through recoverable incongruity, ironic stance, productive morphology, and shared interactional context.