Instant
late Middle English (in instant (sense 2 of the adjective, sense 3 of the adjective, sense 4 of the adjective)): via Old French from Latin instant- ‘being at hand’, from the verb instare, from in- ‘in, at’ + stare ‘to stand’.
wiktionary
From Middle English instant(“infinitely short period of time”), from Old French instant(“assiduous, at hand”, adj), from Latin instans, instant-(“present, pressing, urgent”, literally “standing near”), from in + stāre(“to stand”). Compare Old English instede(“immediately, on the spot, at once”). More at in, stand.
From French instant and Middle English instant, both from Old French, from Latin instans(“standing by, being near, present, also urgent, importunate”), present participle of instō(“to stand upon, press upon, urge, pursue, insist”), from in(“on, upon”) + stō(“to stand”); see state.
etymonline
instant (n.)
late 14c., "moment in time, infinitely short space of time," from noun use of Old French instant "near, immediate, at hand; assiduous, urgent" (see instant (adj.)). Related: Instanted; instanting.
instant (adj.)
mid-15c., "now, present, of the moment, current," from Old French instant "near, imminent, immediate, at hand; urgent, assiduous" (14c.) and directly from Medieval Latin instantem (nominative instans), in classical Latin "present, pressing, urgent," literally "standing near," present participle of instare "to urge, to stand near, be present (to urge one's case)," from in- "in" (from PIE root *en "in") + stare "to stand," from PIE root *sta- "to stand, make or be firm."
Sense of "immediate, done or occurring at once" is from 1590s. Of processed foods, by 1912; instant coffee is from 1915. Televised sports instant replay attested by 1965. Instant messaging attested by 1994.
The word was used 18c.-19c. in dating of correspondence, meaning "the current month," often abbreviated inst. Thus 16th inst. means "sixteenth of the current month" (compare proximo, ultimo).
