Learn Italian: C'era un odoraccio nella stanza. - There was a bad smell in the room.

The suffix -accio is a pejorative, meaning it adds a negative, unpleasant, or ugly quality to a noun. By dropping the final -e of odore (smell) and adding -accio, the word transforms into a single noun meaning "a bad smell" or "stink".

Is it also correct to just say un cattivo odore?

Yes! Un cattivo odore (a bad smell) means the exact same thing. Italians love using suffixes like -accio in everyday conversation because they pack a strong descriptive punch into a single word, but using a noun with an adjective is just as correct.

Why is it un odoraccio without an apostrophe?

Odoraccio is a masculine noun, because its root word odore is masculine. We only use the apostrophe (un') for feminine nouns that start with a vowel. For masculine nouns starting with a vowel, we just use un.

Why use the imperfect c'era (there was) instead of the passato prossimo c'è stato?

The imperfect tense is used here to describe an ongoing condition or to set the scene in the past. You are simply describing what the room was like at the time, rather than talking about a specific, completed action.