Is cousin masculine or feminine in French?

Le cousin. "Cousin" is masculine in French. Nouns ending in -in are usually masculine.

Is cousin masculine or feminine?

lecousin

/lə kuzɛ̃/masculinecousin

The feminine form is cousine

Nouns ending in -in are usually masculine.

(Words ending in -ain, -ein, -oin, -aim, or -uin follow different rules.)

97.4% of -in nouns are masculine

Mon cousin est l'avant-dernier de la lignée.
My cousin is the last man but one in the line.
Il est parti pour rester avec son cousin.
He went to stay with his cousin.
Elle était jalouse du succès de son cousin.
She was envious of her cousin's success.