a little doubt

[Dixie]

Hi there, teachers. I'm reading The Da Vinci Code by Dan Brown and I came up with something that made me hesitate. On chapter 6 of the book, 1st paragraph, it says:

Still lifes, religious scenes and landscapes (...). The narrator is talking about paintings here. Ok, my question is:

Why Still lifes instead of still lives? What happened to the plural of "life"?

[Alan]

A 'still life' is a type of painting (depicting e.g. a bowl of fruit). Its plural is 'still lifes'.