(s) One that is connected with, participates in, tends to make, or does: songster.
(s) One that is: youngster.
(s) Someone who is, or who's connected with, or who something specified.
A suffix denoting the broker (originally a female), especially a person who does one thing with skill or as an occupation; like in spinster (originally, a woman who spins), songster, baxter (= bakester), youngster.
(n) A termination denoting career, as in maltster, gamester, spinster, songster, etc.