Diminutives (-inho/-zinho)

The short answer

The diminutivo (diminutive) adds -inho / -inha or -zinho / -zinha to a word. It can mean small (uma casinha, a little house), but in Brazil it is used far more for warmth and politeness: Espera um minutinho (just a minute), Bora tomar um cafezinho? On adverbs it adds intensity: pertinho (really close), cedinho (nice and early), rapidinho (real quick).

How to form it

The end of the word decides the suffix:

The diminutive keeps the gender of the noun: o pão → o pãozinho, a mãe → a mãezinha. The written accent of the base goes away, because the stress moves to the suffix: café → cafezinho, rápido → rapidinho. The tilde stays, since it marks a nasal sound, not stress: pãozinho, irmãozinho.

Plural. With -inho, just add -s: casinhas, gatinhos. With -zinho, the standard rule puts the base in the plural, drops its -s and adds -zinhos: pães → pãezinhos, flores → florezinhas. In everyday speech you will also hear pãozinhos and, very often, florzinhas.

When to use it

• Small size: uma casinha na praia, um cachorrinho.
• Affection, with names, children and family: Joãozinho, Aninha (Ana), três aninhos, minha filhinha.
• Politeness and softening, to make a request or a wait sound smaller: um minutinho, um favorzinho, um pouquinho, Posso fazer uma perguntinha?
• Intensity on adverbs and some adjectives: pertinho, cedinho, rapidinho, devagarinho, quentinho (nice and warm).
• Fixed words that no longer mean "small": cafezinho (a small black coffee, also hospitality), salgadinho (savoury snack), docinho (party sweet), carrinho (shopping trolley), sozinho (alone).

• Espera um minutinho, já volto.Wait just a minute, I'll be right back.politeness
• Bora tomar um cafezinho?Shall we grab a coffee?café → cafezinho
• A padaria é pertinho daqui.The bakery is really close to here.intensity
• O Joãozinho fez três aninhos ontem.Little João turned three yesterday.affection
• Me vê dois pãezinhos, por favor.Two bread rolls, please.plural: pães → pãezinhos

Contrasts and traps

• Choose by stress, not by spelling: café ends in a stressed vowel, so cafezinho, never cafeinho.
• Keep the hard sounds: pouco → pouquinho, amigo → amiguinho, barco → barquinho.
• No accent on the diminutive: rapidinho, cafezinho, avozinha.
• Tone matters. Diminutives are friendly and very common in speech, service and family talk, but sound out of place in formal writing. Sometimes they even sound ironic: um trabalhinho can mean a small job or a not-very-serious one.
• sozinho means alone, not "a little alone": Moro sozinho.

If you speak Spanish

Brazilian -inho is your -ito, and it is used even more: un minutito → um minutinho, poquito → pouquinho, cerquita → pertinho, rapidito → rapidinho. Spanish -cito becomes -zinho: cafecito → cafezinho, never cafecinho. And -ito itself is not Portuguese: um minutito sounds Spanish.