The official suffix -op- turns a number into the size of a group. Triopo is one group containing three members, triopa describes something made up of three members, and triope describes people acting or arranged together in threes. The number before -op- always states how many members the group has.
This differs from merely counting three people, distributing three items to each person, repeating something three times, or multiplying a quantity by three. English can express several of those meanings with in threes, three-person, or threefold, so the Esperanto semantic head matters. All unlabelled uses below are neutral contemporary Esperanto.
The number becomes a group size
-Op- attaches only to numerals and number-like quantity words. A grammatical ending then determines how the grouped meaning functions:
| Form | Word class | Meaning |
|---|---|---|
| kvaropo | noun | a group of four |
| kvaropa | adjective | consisting of four members |
| kvarope | adverb | together/in groups of four |
Kvaropo da muzikistoj ludis apud la enirejo.
A group of four musicians played beside the entrance.
La lernejo kreis kvaropan teamon por la konkurso.
The school formed a four-member team for the competition.
La kursanoj diskutis kvarope dum dek minutoj.
The course participants discussed in groups of four for ten minutes.
In each form, kvar gives the membership count. The resulting noun, adjective, or adverb—not the bare numeral—is the semantic head. This tight restriction is important: -op- does not attach productively to ordinary nouns or qualities.
Cardinal quantity versus a grouped unit
A bare cardinal answers “how many individuals?” An -op- form asks the listener to treat those individuals as one grouping:
Tri teknikistoj venis por kontroli la sistemon.
Three technicians came to inspect the system.
Triopo da teknikistoj venis kiel unu inspekta teamo.
A group of three technicians came as one inspection team.
The first subject is grammatically plural: tri teknikistoj venis. In the second, the head triopo is singular even though it contains three people: triopo venis. The members commonly follow with da when their type is introduced: triopo da teknikistoj. A de phrase can identify a known source group: la triopo de nia sekcio.
An -op-o noun takes ordinary plural and accusative endings. Two groups of three are du triopoj as a subject and du triopojn as an object.
La organizantoj elektis du triopojn por la fina rondo.
The organizers selected two groups of three for the final round.
English speakers sometimes let the embedded number control agreement. Esperanto does not: grammatical agreement follows the singular or plural group noun, just as with other collective nouns.
Unuopa and unuope: each viewed separately
The most lexicalized member of the family is built from unu. Unuopo is one individual, unuopa means individual or single when members are considered separately, and unuope means one at a time or each separately.
Bonvolu eniri unuope, por ke ni povu kontroli ĉiun bileton.
Please enter one at a time so that we can check each ticket.
Ni publikigos la ĝeneralan rezulton, sed ne la unuopajn respondojn.
We will publish the overall result, but not the individual responses.
This is not redundant with plain unu. Unu gasto eniris counts one guest; la gastoj eniris unuope says that multiple guests entered separately, one after another. The grouping perspective remains present even when the group size is one.
Duo, trio, and explicit duopo, triopo
Number words with -o can already name either a number or, contextually, a group. Duo and trio are especially common for a musical pair or trio. The explicit duopo/triopo foregrounds group structure but is not always required.
La ĵaza trio prezentos sian novan albumon ĉi-vespere.
The jazz trio will present its new album this evening.
La gvidanto dividis nin en duopojn por la interparola ekzerco.
The leader divided us into pairs for the conversation exercise.
Paro is another established word for two things naturally paired: paro da ŝuoj, geedza paro. Duopo is the systematic numerical choice for a deliberately formed two-member group. Neither word is a universal replacement for the other.
For larger sizes, explicit -op- prevents ambiguity: kvinopo, dekopo, dekduopo. A bare deko can mean the number ten, a set of ten, or an approximate ten in some contexts; dekopo clearly profiles the group.
The adverb tells how participants act together
Adverbs in -ope modify the manner or arrangement of an action. They do not count how many times the action occurs.
La ekskursantoj revenis duope al la buso.
The excursion participants returned to the bus in pairs.
Ni laboros kvinope: du esploros, du verkos, kaj unu redaktos.
We will work as a group of five: two will research, two will write, and one will edit.
— Kiomope ni faru la taskon? — Triope, sed unu grupo havos kvar lernantojn.
— In groups of how many should we do the task? — In threes, but one group will have four students.
Kiomope? asks the group size. Multope says “many together” or “in large numbers” without an exact count.
Post la anonco volontuloj aliĝis multope.
After the announcement, volunteers signed up in large numbers.
These forms show why -op- also accepts number-like correlatives and quantity expressions, not arbitrary descriptive roots.
Grouping, distribution, multiplication, and repetition
Four nearby patterns answer different questions:
| Form | Question answered | Example meaning |
|---|---|---|
| triope | in groups of how many? | in threes |
| po tri | how many for each? | three each |
| trioble | by what factor? | threefold |
| trifoje | on how many occasions? | three times |
La gastoj sidis duope, kaj ĉiu paro ricevis po unu menuon.
The guests sat in pairs, and each pair received one menu.
Duope describes the arrangement of the guests; po unu distributes a menu to each pair. For the distribution system, see po.
La komisiono estas kvinopa, sed ĝia buĝeto estas duoble pli granda ol pasintjare.
The committee has five members, but its budget is twice as large as last year.
Here kvinopa counts members; duoble gives a multiplication factor. A familiar object made of two corresponding layers or parts also normally uses -obl-: duobla lito, duobla fenestro, not duopa lito in those conventional senses.
La lernantoj legis la dialogon duope kaj poste ripetis ĝin dufoje.
The students read the dialogue in pairs and then repeated it twice.
The same people can act duope on each of two occasions. The suffixes do not compete; they encode different semantic axes.
Compounding and spelling
The whole numeral precedes -op- and forms one derived word. Dekduopa means twelve-member. With a long numeral, hyphens may preserve the original word boundaries: dudek-kvinopa delegacio. This is a clarity device, especially in (formal) administrative writing.
La konferenco akceptis dudek kvinopajn teamojn.
The conference accepted twenty five-member teams.
La konferenco akceptis dudek-kvinopan delegacion.
The conference accepted a twenty-five-member delegation.
The first contains cardinal dudek plus plural adjective kvinopajn: twenty teams, each five-member. The second contains one adjective based on twenty-five: one delegation with twenty-five members. Preserving English spacing would hide that scope contrast.
Productivity and conventional limits
Any sensible group size can be formed, but a grammatical derivative is not automatically the normal label for an object. Triopa laborgrupo is transparent because a working group has three members. A “double room” is conventionally dupersona ĉambro or ĉambro por du personoj, not necessarily duopa ĉambro, because room capacity is not always conceptualized as a membership group.
In (formal) rules, state both the unit and the members when legal or organizational precision matters: kvinopa komisiono, konsistanta el.... Productive morphology makes the count clear; it does not identify who qualifies as a member.
Common Mistakes
Using -op- for simple counting
❌ Mi elektis kvaropon da tomatoj por la saŭco.
Incorrect for simply choosing four independent tomatoes.
✅ Mi elektis kvar tomatojn por la saŭco.
I chose four tomatoes for the sauce.
Confusing grouping with distribution
❌ La instruisto disdonis triope foliojn al ĉiu grupo.
Incorrect — triope describes acting in groups of three, not three items per recipient.
✅ La instruisto disdonis po tri foliojn al ĉiu grupo.
The teacher handed out three sheets to each group.
Confusing grouping with repetition
❌ La gastoj eniris dufoje kaj marŝis unu apud la alia.
Incorrect for one entrance made in pairs — dufoje says the entrance occurred twice.
✅ La gastoj eniris duope kaj marŝis unu apud la alia.
The guests entered in pairs and walked beside one another.
Letting the members control the group noun's number
❌ La triopo da muzikistoj estis lacaj.
Incorrect agreement — the grammatical head triopo is singular.
✅ La triopo da muzikistoj estis laca.
The group of three musicians was tired.
Separating one derived group adjective
❌ Ili elektis dek du opan ĵurion.
Incorrect spacing for one twelve-member jury.
✅ Ili elektis dekduopan ĵurion.
They selected a twelve-member jury.
Key Takeaways
-Op- turns a numeral into group size: -opo names the group, -opa describes its membership count, and -ope describes acting or arranging in such groups. Use a cardinal for simple quantity, po for equal distribution, -obl- for multiplication, and fojo for separate occasions. Put the complete number before the suffix and let the resulting group noun control agreement.
Now practice Esperanto
Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.
Start learning Esperanto →Related Topics
- -obl-: Multiplicative QuantityB1 — Use -obl- for multiplication factors and multiple structure, while separating magnitude from repeated occasions, group size, and fractions.
- -foj-: Number Of OccasionsB2 — Use fojo and compact -foj- compounds to count occasions, distinguishing repetition from multiplication, duration, grouping, and ordinal sequence.
- Collective and Group NumbersB1 — Describe groups of a stated size with -op-, distinguishing group structure from simple quantity, distribution, and multiplication.
- Cardinal NumbersA1 — Use Esperanto cardinal numbers to count, quantify noun phrases, identify items, and read basic dates, times, measurements, and decimal notation.
- Collective NounsB1 — How singular Esperanto nouns name groups, how -ar- builds collections, and when a collective itself becomes plural.
- PoB2 — Use po before a repeated quantity to distribute equal shares, rates, or amounts across people, things, places, or occasions.