(1):

(n.) One who disciplines; one who excels in training, especially with training, especially with regard to order and obedience; one who enforces rigid discipline; a stickler for the observance of rules and methods of training; as, he is a better disciplinarian than scholar.

(2):

(n.) A Puritan or Presbyterian; - because of rigid adherence to religious or church discipline.

(3):

(a.) Pertaining to discipline.