Words at Play : The Real History Behind 10 Game of Thrones Words
Maesters are scholars who act as physicians, tutors, and advisors to the noble houses of Westeros. Upon completion of his training, a Maester swears to serve the castle he is assigned to, whoever may hold the castle.
Maester resembles the English word master in both form and meaning. The original meaning of the English word is "a male teacher or tutor," and one of the primary duties of a maester is to teach the children of the house.