1640s, "practicing rigorous self-denial as a religious exercise," from Latinized form of Greek asketikos "rigorously self-disciplined, laborious," from asketes "monk, hermit," earlier "skilled worker, one who practices an art or trade," especially "athlete, one in training for the arena," from askein "to exercise, train," especially "to train for athletic competition, practice gymnastics, exercise," perhaps originally "to fashion material, embellish or refine material."
The Greek word was applied by the stoics to the controlling of the appetites and passions as the path to virtue and was picked up from them by the early Christians. Figurative sense of "unduly strict or austere" also is from 1640s. Related: Ascetical (1610s).
1650s, "one rigorous in self-denial," especially as an act of religious devotion; 1670s, Ascetic, "one of the early Christians who retired to the desert to live solitary lives of meditation, self-denial, and prayer," from ascetic (adj.).