Which lexical class does "wont" fall into in this sentence?

As he is wont to do.

Is "wont" an adjective, noun, verb, or something else in this context? How would you determine which lexical class wont falls into in any given sentence, since it can be used as an adjective, noun, or verb?


It’s a predicative adjective, meaning ‘accustomed to’, or ‘used to’.