How do you say rest in Latin?

The verb "to rest" is requiescere. The corresponding noun is requies (genitive requietis, sometimes requiei, f.). The "rest of" something is reliquus, -a, -um. Note that Latin doesn't say "the rest of something"; reliquus is an adjective that agrees with the noun, and is used more or less like the English adjective "remaining": reliquum diem, "for the rest of the day [the remaining day]".