To maroon is to strand someone in an isolated place, often a deserted island. Think of "Gilligan's Island," "Survivor," or "Lost" — TV shows that feature folks marooned on islands — and you've got the idea.
Maroon can be a noun or verb, depending on how you use it. If you maroon your best friend on a deserted island, in addition to being a terrible friend, you're using the word as a verb. If this friend was wearing a brownish-red shirt at the time he was marooned, you would use the adjective maroon to describe the shirt's color.