Comment by Biganon

Funny tidbit: "missile" used to be an adjective, "a missile weapon" = "a weapon than can be sent/thrown".

Same with cereals, "cereal" was an adjective that meant "relative to the goddess Ceres" then "relative to bread/wheat". "Cereal plants" -> cereals.

It's called "nominalization (or substantivization) by ellipsis".