Something apt is perfectly appropriate, clever and well-suited to the matter at hand. If your room is small and dark, “cave-like” would be an apt description.
The wee cousin of aptitude, apt has the same root meaning of "strength and ideal appropriateness." An apt description or nickname is one that’s just right. Apt can also be used in the form "to be apt to" meaning "to be likely to" do something. You’re apt to use this word more now that you know precisely what it means!