Adjectives agree with their nouns in gender and number. Plural adjectives take the spirant mutation to agree with plural nouns. Feminine adjectives take the soft mutation when following feminine nouns.
Adjectives tend to follow the noun. Only the adjectives bon, good, and mal, bad, can be used without any uncertainty before a noun.
When an adjective precedes a noun it has a figurative rather than a literal meaning. This effects only a couple of adjectives: pwbr, poor, has the meaning of `destitute' after the noun, lla blenhin bwbr, the poor child (who has no lunch money), but unfortunate when it comes before the noun, lla bwbr blenhin, the poor child (who just got bullied for her lunch money). Likewise with gran, big, large, when it precedes the noun it means importance, not size:
Swl can come before or after the noun with a difference in meanings. After the noun it means lonely, yn blenhin swl, a lonely child. Before a noun, it means only, yn swl blenhin, an only child.
Brithenig can use an adjective as a noun by putting an article in front of it. It then refers to an object that has that quality: ill rhys, the red one; llo phwg, the little ones.
For a comparative of an adjective, Brithenig puts the words ply, more and min, less before an adjective, with the spirant mutation of the initial consonant of the following adjective. 'Than' is translated as ca: ply h-allt ca yn gas, `taller than a house'.
The superlative is formed by putting the definate article suitable for the gender of the noun before the comparative adjective: ill ply h-allt, the tallest. When a noun is qualified, the definate article goes in front of the noun, replacing yn: lla gas bly h-allt, the tallest house. It is omitted if the noun is proceeded by a possessive pronoun:
Most adverbs are derived from adjectives by adding the ending -fent. In spoken Brithenig this is usually pronounced `fen' but the t is still written: