Common Prefixes | Portuguese (Brazil) Grammar

A prefix is a meaning glued to the front of a word: fazer (to do) becomes refazer (to redo), desfazer (to undo), contrafazer (to counterfeit). For an English speaker this is the friendliest corner of Portuguese word formation, because nearly every prefix is a shared Latin morpheme you already know from English — re-, in-, sub-, super-, anti-. The prefix almost never changes the word's grammatical class (a verb stays a verb, a noun stays a noun); it just adjusts the meaning. This page maps the productive prefixes by what they do, and explains the post-AO90 hyphenation rules that decide whether to write antibiótico or anti-inflamatório.

Why prefixes are the easy win

Unlike suffixes — which change word class and force gender/number agreement — prefixes mostly leave the base word's grammar untouched. You bolt the meaning on the front and keep going. And because Portuguese and English inherited the same Latin prefixes, the meanings transfer almost wholesale.

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If you can read English words like redo, impossible, subway, international, and superhuman, you already know the meanings of re-, im-, sub-, inter-, and super- in Portuguese. The work is learning the spelling and the hyphenation, not the meaning.

Negation and reversal

This is the densest and most useful family. Three prefixes do most of the work.

Prefix	Meaning	Attaches to	Examples	English match
des-	reverse / undo / remove	verbs, nouns, adjectives	fazer → desfazer; ligar → desligar; honesto → desonesto	un- / dis-
in- / im- / i- / ir-	not (negation)	adjectives, nouns	feliz → infeliz; possível → impossível; legal → ilegal; regular → irregular	in- / im- / il- / ir-
a- (an-)	without / lacking	adjectives, nouns	moral → amoral; político → apolítico; normal → anormal	a- / an-

des- — the great reverser (and a BR favorite)

Des- is the most productive prefix in Brazilian Portuguese. It reverses an action (fazer → desfazer, "undo"), removes something (cabelo → descabelado, "disheveled"), or simply negates (honesto → desonesto). Crucially, it's the everyday word for switching things off: desligar (turn off), desconectar (disconnect), deslogar (log out).

Pode desligar a televisão? Quero dormir.

Can you turn off the TV? I want to sleep. (des- 'reverse' + ligar 'turn on')

Tive que desfazer tudo e começar de novo.

I had to undo everything and start over. (des- + fazer)

Não confio nele; acho ele meio desonesto.

I don't trust him; I find him a bit dishonest. (des- + honesto)

in- / im- / i- / ir- — negation that assimilates

This prefix negates adjectives, and its form changes to match the following sound — exactly like English. Before p and b it becomes im- (impossível, imberbe); before l it assimilates to i- (ilegal, ilógico); before r it becomes ir- (irregular, irresponsável); elsewhere it stays in- (incapaz, infeliz).

É impossível terminar isso hoje, é incapaz de funcionar assim.

It's impossible to finish this today, it's incapable of working like this. (im- before p, in- before c)

Estacionar aqui é ilegal e totalmente irresponsável.

Parking here is illegal and totally irresponsible. (i- before l, ir- before r)

The assimilation isn't arbitrary — it's the sound system smoothing the prefix into the base, the same reason English says impossible not inpossible. (For the full negation picture, including non-prefix negation, see negation/negative-prefixes.)

a- — "without," in learned words

The a- (or an- before a vowel) prefix means "lacking" and shows up mostly in academic and technical vocabulary: amoral (without morals — different from imoral, "immoral"), apolítico (apolitical), atípico (atypical), anônimo (anonymous).

Ele se diz apolítico, mas vota em toda eleição.

He calls himself apolitical, but he votes in every election. (academic)

Repetition — re-

Re- means "again" or "back," just as in English. It's freely productive: take almost any verb and prefix re- to mean "do it again." Fazer → refazer (redo), ler → reler (reread), começar → recomeçar (restart), escrever → reescrever (rewrite).

Vou ter que reescrever o e-mail inteiro.

I'm going to have to rewrite the whole email. (re- + escrever)

Reli o livro e gostei ainda mais.

I reread the book and liked it even more. (re- + ler)

Intensity — super-, hiper-, mega-, ultra-, arqui-

These boost the base word, and in colloquial Brazilian Portuguese they're sprayed around freely for emphasis. Super- in particular has become an all-purpose intensifier in casual speech (super legal, "super cool"). The set also includes hiper-, mega-, ultra-, and the more learned arqui- (arqui-inimigo, archenemy).

A festa foi superdivertida; o lugar era megacaro, mas valeu.

The party was super fun; the place was mega-expensive, but it was worth it. (informal intensifiers)

É um produto ultramoderno e hipersofisticado.

It's an ultramodern and hyper-sophisticated product.

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In casual Brazilian speech, super- often detaches and behaves like an adverb: "Achei ela super simpática" ("I found her super nice"). This is informal — in writing, prefer the joined form or a standard adverb like muito.

Position and relation — sub-, sobre-, entre-, ante-, pré-, pós-, inter-

These locate the base word in space, time, or hierarchy, and again they match English closely.

Prefix	Meaning	Examples	English match
sub-	under / below	subsolo, subestimar, submarino	sub-
sobre-	over / on top / excess	sobrecarga, sobrenatural, sobreviver	over- / super-
inter-	between / among	internacional, intercâmbio, intervir	inter-
entre-	between (native form)	entreato, entrelinhas, entreaberto	inter- / between
ante-	before (in time/space)	anteontem, antessala, antecipar	ante- / pre-
pré-	before / pre-	pré-história, prévia, pré-pago	pre-
pós-	after / post-	pós-graduação, pós-guerra	post-
anti-	against	antibiótico, antivírus, antissocial	anti-
contra-	against / counter	contradizer, contramão, contraproposta	counter- / contra-
co-	with / joint	colaborar, coautor, coexistir	co-
mal- / mau-	bad(ly)	mal-educado, malsucedido, mal-entendido	mis- / mal-

Estou fazendo pós-graduação em economia internacional.

I'm doing a postgraduate degree in international economics. (pós- 'after' + inter- 'between')

Ele dirigiu na contramão e quase causou um acidente.

He drove the wrong way down the street and almost caused an accident. (contra- 'against' + mão 'direction')

Foi tudo um mal-entendido; ninguém quis te ofender.

It was all a misunderstanding; nobody meant to offend you. (mal- 'bad' + entendido 'understood')

Hyphenation: the post-AO90 rule that matters most

The 1990 Orthographic Agreement (in force in Brazil) tightened the hyphenation rules for prefixes. You can ignore most of the fine print and remember one core rule that covers the majority of cases:

Use a hyphen when the prefix ends in the same letter the base word begins with — most often a doubled vowel, or the combination of a prefix and a base starting in h.

Situation	Hyphen?	Example
prefix ends in vowel + base starts with the SAME vowel	YES	anti-inflamatório, micro-ondas, contra-ataque
prefix ends in vowel + base starts with a DIFFERENT vowel	no (join)	antiaéreo, autoescola, extraescolar
base starts with H	YES	anti-higiênico, super-homem, pré-história
prefix ends in R + base starts with R (super-, hiper-, inter-)	YES	super-resistente, hiper-realista, inter-racial
prefix ends in consonant + base starts with different letter	no (join)	superinteressante, hipermercado, subsolo
pré-, pós-, pró- (stressed, with accent)	YES always	pré-pago, pós-guerra, pró-ativo

Tomei um anti-inflamatório porque o joelho inchou.

I took an anti-inflammatory because my knee swelled up. (anti- + i = doubled vowel → hyphen)

Esquentei a comida no micro-ondas.

I heated the food in the microwave. (micro- + o = doubled vowel → hyphen)

Esse tecido é superinteressante e antialérgico.

This fabric is super interesting and hypoallergenic. (different vowels and consonant → joined, no hyphen)

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Two famous AO90 traps: it's micro-ondas (with hyphen, because micro- ends in o and ondas begins with o), and it's autoescola (no hyphen, because auto- ends in o but escola begins with e — different vowels). When in doubt, ask: "Do the prefix's last letter and the base's first letter match?" If yes, hyphenate. (Full details at spelling/hyphenation-rules.)

Common Mistakes

❌ Esqueci de deslogar... quer dizer, de inligar a TV?

Confusion — 'turn off' is desligar (des- reverses ligar 'turn on'); there's no 'in-ligar'.

✅ Esqueci de desligar a TV.

I forgot to turn off the TV.

❌ É inpossível chegar a tempo.

Incorrect — in- assimilates to im- before p: impossível.

✅ É impossível chegar a tempo.

It's impossible to arrive on time.

❌ Comprei um microondas novo.

Incorrect — micro- + ondas needs a hyphen (doubled o): micro-ondas.

✅ Comprei um micro-ondas novo.

I bought a new microwave.

❌ Ela está fazendo posgraduação.

Incorrect — pós- always takes its accent and a hyphen: pós-graduação.

✅ Ela está fazendo pós-graduação.

She's doing a postgraduate degree.

❌ Que pessoa maleducada!

Incorrect — mal- before a vowel takes a hyphen: mal-educada.

✅ Que pessoa mal-educada!

What a rude person!

Key Takeaways

Prefixes attach to the front of a word and adjust meaning without changing word class — the easiest corner of word formation for English speakers, since most are shared Latin morphemes.
Negation/reversal: des- (undo/turn off — the most productive in BR), in-/im-/i-/ir- (negation, assimilating to the next sound), a- (without, in learned words).
Repetition: re- ("again"), freely productive on almost any verb.
Intensity: super-, hiper-, mega-, ultra- — sprayed around casual BR speech for emphasis.
Position/relation: sub-, sobre-, inter-, ante-, pré-, pós-, anti-, contra-, co-, mal-.
Hyphenation (AO90): hyphenate when the prefix's last letter equals the base's first letter (anti-inflamatório, super-resistente), before h (super-homem), and always with stressed pré-/pós-/pró-. Otherwise join (antiaéreo, superinteressante).

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