Old English into "into, to, against, in," originally in to. It emerged in late Old English to do the work of the dative case inflections, then fading, that formerly distinguished, for instance, the notion of "in the house" from that of "into the house." Compare onto, unto. To be into (something) "be intensely involved in or devoted to" recorded by 1967 in American English youth slang.
"toward and upon; to and in connection with; to the top of," 1580s, on to, from on + to. It appeared much later than parallel into, unto. As a closed compound, onto (on analogy of into), it is recorded from 1715. "The word is regarded by purists as vulgar, and is avoided by careful writers" [Century Dictionary, 1895].
the reading of one's own ideas into scripture, 1859, from Greek eis "in, into" + ending from exegesis. Related: Eisegetical.
"act of forming into regiments; state of being formed into classified systems," 1856, noun of action from regiment (v.).
"to form into a cake" (transitive), c. 1600; "to concrete into a hard mass" (intransitive), 1610s; from cake (n.). Related: Caked; caking.
c. 1600, "press closely into something," from Latin impactus, past participle of impingere "to push into, drive into, strike against," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + pangere "to fix, fasten" (from PIE root *pag- "to fasten"). Original sense is preserved in impacted teeth. Sense of "strike forcefully against something" first recorded 1916. Figurative sense of "have a forceful effect on" is from 1935. Related: Impacting.
1705, "to divide into classes, place in ranks or divisions," from class (n.) or French classer. Sense of "to place into a class" is from 1776. Related: Classed; classing.
"to break into," 1805 (implied in irrupted), back-formation from irruption or else from Latin irruptus, past participle of irrumpere "to break in, burst into."