gender

in "je veux une boisson froide" , is une used because boisson is feminine or bcos froide is feminine? I noted before that nouns which end in vowels are feminine, but froide is adjective so a bit confused!

Boisson is a feminine noun (la boisson), and is an exception like la couleur (the color) or le jeu (the game).

Salut! Boisson is a feminine noun. Une is used because boisson is feminine and then the adjective that follows the noun must also agree with it, therefore it is "une boisson froide" as opposed to "une boisson froid" which in incorrect. I hope this helps! - Marie-Claire