This is the 2318th most frequent French word.
noirs
"Noirs" means "blacks" in English, typically referring to the color or black people.
In this sentence, 'noirs' is used as an adjective describing the color of the cats, agreeing in gender and number with the plural noun 'chats'.
Les chats noirs sont souvent associés à la magie.
Black cats are often associated with magic.
Here, 'noirs' is an adjective describing 'cheveux', and it adheres to the singular masculine form as 'cheveux' is a singular masculine noun in appearance but plural semantically.
Ses cheveux noirs brillent sous le soleil.
Her black hair shines under the sun.
'Noir' in this sentence is an adjective modifying the singular masculine noun 'costume', agreeing in gender and number.