Oneself

wiktionary

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A contracted form of one's self. Equivalent to one +‎ -self.

etymonline

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oneself

1540s, one's self, "a person's self" (without distinction of gender), an emphatic form of one, with self. Hyphenated 18c.; written as one word from c. 1827, on model of himself, herself, myself, itself, etc.