methinks v.

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.

Old English þencan "imagine, conceive in the mind; consider, meditate, remember; intend, wish, desire" (past tense þohte, past participle geþoht), probably originally "cause to appear to oneself," from Proto-Germanic *thankjan (source also of Old Frisian thinka, Old Saxon thenkian, Old High German denchen, German denken, Old Norse þekkja, Gothic þagkjan).

Old English þencan is the causative form of the distinct Old English verb þyncan "to seem, to appear" (past tense þuhte, past participle geþuht), from Proto-Germanic *thunkjan (source also of German dünken, däuchte). Both are from PIE *tong- "to think, feel" which also is the root of thought and thank.

The two Old English words converged in Middle English and þyncan "to seem" was absorbed, except for its preservation in archaic methinks "it seems to me."

As a noun, think, "act of prolonged thinking," is attested by 1834. The figurative thinking cap is attested from 1839.