Adjectives in Irish tend to follow the word they are describing, unlike English, which usually puts the adjective in front of the word: big house, instead of teach mhór (lit., house big).

fíon — wine
fíon dearg — red wine

A few adjectives are automatically attached to the word they describe. Sean (old) and droch (bad) are two of these.

bean — woman
seanbhean — old woman, crone

Adjectives are considered masculine or feminine, and singular or plural depending on the noun they follow, and gender and number can change the words, as we've seen in other cases.

feminine singular nouns cause lenition in the adjective
masculine plural nouns that end in a consonant cause lenition in the adjective
nouns that end in a vowel do not change the following adjective

Adjectives are made plural by adding the suffix -a or an -e to the word. If the last consonant in the word is broad (preceded/followed by a, o, or u), then add 'a'. If the last consonant in the word is slender, then add a -e.

last consonant is broad (a,o,u) — add -a
last consonant is slender (i,e) — add -e

Finally, when counting objects, the singular form of the adjective is used when counting one thing, or counting more than 20 things. The plural form is used for counting two to nineteen objects.