Inkling
late Middle English (in the sense ‘a mention in an undertone, a hint’): from the rare verb inkle ‘utter in an undertone’, of unknown origin.
wiktionary
From Middle English ningkiling, nyngkiling(“hint, slight indication; mention, whisper”), [1] and then either:
From inkle + -ing.
etymonline
inkling (n.)
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.)).
