Clue: phonetic variant of clew (q.v.) “a ball of thread or yarn,” with reference to the one Theseus used as a guide out of the Labyrinth. The purely figurative sense of “that which points the way” is from 1628. Clueless is from 1862.
Sleuth: c.1200, “track or trail of a person,” from O.N. sloð “trail,” of uncertain origin. Meaning “detective” is 1872, shortening of sleuthhound “keen investigator” (1849), a figurative use of a word for a kind of bloodhound that dates back to 1375. The verb (intrans.) meaning “to act as a detective, investigate” is recorded from 1912.
