adv. Once. [ Obs. ] Chaucer. [ 1913 Webster ]
pron. A reflexive form of the indefinite pronoun one. Commonly written as two words, one's self. [ 1913 Webster ]
One's self (or more properly oneself), is quite a modern form. In Elizabethan English we find a man's self = one's self. Morris. [ 1913 Webster ]