Initial
early 16th century: from Latin initialis, from initium ‘beginning’, from inire ‘go in’, from in- ‘into’ + ire ‘go’.
wiktionary
From Middle French initial or straightway from its Latin etymon initiālis(“of the beginning, incipient, initial”), from initium(“a going in, entrance, beginning”), from inire(“to go in, enter upon, begin”), from in(“in”) + ire(“to go”).
etymonline
initial (adj.)
1520s, "of or pertaining to a beginning," from French initial or directly from Latin initialis "initial, incipient, of the beginning," from initium "a beginning, a commencement; an entrance, a going in," noun use of neuter past participle of inire "to go into, enter upon, begin," from in- "into, in" (from PIE root *en "in") + ire "to go" (from PIE root *ei- "to go"). Related: Initially.
initial (v.)
"to mark or sign with initials," 1837, from initial (n.). Related: Initialed; initialing.
initial (n.)
"initial letter of a name or surname," 1620s, from initial (adj.) in a specialized sense "standing at the beginning of a word, sentence, etc." (1620s).
