myself (pron.)

a pronoun of the first person in oblique cases, Old English me (dative), me, mec (accusative); oblique cases of I, from Proto-Germanic *meke (accusative), *mes (dative), source also of Old Frisian mi/mir, Old Saxon mi, Middle Dutch mi, Dutch mij, Old High German mih/mir, German mich/mir, Old Norse mik/mer, Gothic mik/mis; from PIE root *me-, oblique form of the personal pronoun of the first person singular (nominative *eg; see I); source also of Sanskrit, Avestan mam, Greek eme, Latin me, mihi, Old Irish me, Welsh mi "me," Old Church Slavonic me, Hittite ammuk.

Erroneous or vulgar use for nominative (such as it is me) is attested from c. 1500. The dative is preserved in obsolete meseems, methinks and expressions such as sing me a song ("dative of interest"). Reflexively, "myself, for myself, to myself" from late Old English. The expression me too indicating the speaker shares another person's experience or opinion, or that the speaker wants the same as another is getting, is attested by 1745. In the 1880s it was a derisive nickname of U.S. politician Thomas C. Platt of New York, implying that he was a mere echo and puppet of fellow U.S. Senator Roscoe Conkling, and in mid-20c. it often was a derogatory term, especially in U.S. politics (me-too-ism).

The political "me-too-ism," abjectly displayed by the "conservatives" of today toward their brazenly socialistic adversaries, is only the result and the feeble reflection of the ethical "me-too-ism" displayed by the philosophers of the nineteenth and twentieth centuries, by the alleged champions of reason, toward the Witch Doctors of morality. [Ayn Rand, "For the New Intellectual," 1961]

The #MeToo movement calling attention to and opposing sexual harassment and assault, became prominent in October 2017.

"belonging to me," c. 1200, mi, reduced form of mine used before words beginning in consonants except h- (my father, but mine enemy), and from 14c. before all nouns. Always used attributively, mine being used for the predicate. As interjection, by 1825, probably a shortened form of my God!

Old English self, sylf (West Saxon),  seolf (Anglian), "one's own person, -self; own, personal; same, identical," from Proto-Germanic *selbaz (source also of Old Norse sjalfr, Old Frisian self, Dutch zelf, Old High German selb, German selb, selbst, Gothic silba), Proto-Germanic *selbaz "self," from PIE *sel-bho-, suffixed form of root *s(w)e-, pronoun of the third person and reflexive (referring back to the subject of a sentence), also used in forms denoting the speaker's social group, "(we our-)selves" (see idiom).

Its use as the second element in compounded reflexive pronouns (herself, etc.) was in Old English, from the original independent (and inflected) use of self following personal pronouns, as in ic selfa "myself," min selfes "of myself." With a merging of accusative, dative, and genitive cases.

As a noun from c. 1200 as "the person or thing previously specified;" early 14c. as "a person in relation to that same person." G.M. Hopkins used selve as a verb, "become or cause to become a unique self" (1880) but its use seems to have been restricted to poets.