Clue
late Middle English: variant of clew. The original sense was ‘a ball of thread’; hence one used to guide a person out of a labyrinth. clue (sense 1 of the noun) dates from the early 17th century.
wiktionary
Variant of clew(“a ball of thread or yarn”), from Middle English clewe, from Old English clīewen(“ball”), from Proto-Germanic *kliuwīną, *klewô(“ball, bale”), from Proto-Indo-European *glew-(“to amass, conglomerate; clump, ball, bale”). Sense evolution with reference to the one which the mythical Theseus used to guide him out of the Minotaur's labyrinth. More at clew.
etymonline
clue (n.)
"anything that guides or directs in an intricate case," 1590s, a special use of a revised spelling of clew "a ball of thread or yarn" (q.v.). The word, which is native Germanic, in Middle English was clewe, also cleue; some words borrowed from Old French in -ue, -eu also were spelled -ew in Middle English, such as blew, imbew, but these later were reformed to -ue, and this process was extended to native words (hue, true, clue) which had ended in a vowel and -w. The spelling clue is first attested mid-15c.
The sense shift is originally in reference to the clew of thread given by Ariadne to Theseus to use as a guide out of the Labyrinth in Greek mythology. The purely figurative sense of "that which points the way," without regard to labyrinths, is from 1620s. As something which a bewildered person does not have, by 1948.
Thus hardy Theseus, with intrepid Feet,
Travers'd the dang'rous Labyrinth of Crete;
But still the wandring Passes forc'd his Stay,
Till Ariadne's Clue unwinds the Way
[Gay, "Trivia"]
The board game (originally Cluedo) was launched in 1949 in Britain.
clue (v.)
"to indicate by means of a clue," 1934; "to inform someone of the important facts," usually with in, 1948, from clue (n.). Related: Clued; cluing. Earlier in now-obsolete sense of "follow or track by clues" (1660s). In nautical use, "to haul up (a sail) by means of the clue-lines," from clue (n.) in the "wound ball of yarn" sense.
