Learn Italian: C'era un odore sgradevole e il letto era scomodo. - There was an unpleasant smell and the bed was uncomfortable.

The prefix s- is a very common way to make a word mean its exact opposite. Here, it attaches to the adjectives gradevole (pleasant) and comodo (comfortable) to create sgradevole (unpleasant) and scomodo (uncomfortable).

Are there rules for when to use the negative prefix s- instead of in- or dis-?

The s- prefix is only ever attached to words that start with a consonant. You will often see it before consonants like the c in comodo or the g in gradevole. While you still have to memorize which words take which prefix, knowing that s- never goes before a vowel helps narrow it down!

Why do sgradevole and scomodo have different endings, even though they both describe masculine singular nouns?

Italian adjectives generally fall into two categories. Scomodo comes from a standard adjective that changes its ending to match gender (-o for masculine singular). Sgradevole, however, belongs to the group of adjectives that always end in -e in the singular, regardless of whether they describe a masculine noun (like odore) or a feminine one.

Why do we use the imperfect verbs and here instead of the passato prossimo?