c. 1400, apparently from the gerund of the Middle English verb inclen "utter in an undertone, hint at, hint" (mid-14c.), which is of unknown origin; perhaps it is related to Old English inca "doubt, suspicion, question, scruple." However the earliest record of the word is as a nyngkiling; and The Middle English Compendium offers that this is not a misdivision of an inkling but rather suggests the word is a nasalized variant of nikking "a hint, slight indication," gerundive of the Middle English verb nikken "to mark (a text) for correction" (mid-15c.), from nik (n.) "a notch, tally" (see nick (n.)).
"a slight push with the elbow," 1787, from nudge (v.). Figurative sense of "a signal or hint intended to call attention, remind, etc." is by 1831.
"to push slightly with the elbow," 1670s, perhaps from Scandinavian (compare Norwegian nugge, nyggje "to jostle, rub;" Icelandic nugga "to rub, massage"). Figurative sense of "give a hint or signal to," as by a covert touch, is by 1831. Related: Nudged; nudging.
early 15c., "readiness" (in phrase in prompte), from Latin promptus (see prompt (v.)). Meaning "hint, information suggested, act of prompting" is from 1590s. The computer sense of "message given by a computer requiring or helping the user to respond" is by 1977.
"warning, hint of caution," 1550s, Latin, literally "let him beware," 3rd person singular present subjunctive of cavere "to beware, take heed, watch, guard against," from PIE root *keu- "to see, observe, perceive." Legal sense "public warning preventing some action" is from 1650s.