What is the X in X-mas?
1510s, "one who steers a ship," from Middle French pillote (16c.), from Italian piloto, supposed to be an alteration of Old Italian pedoto, which usually is said to be from Medieval Greek *pedotes "rudder, helmsman," from Greek pedon "steering oar," related to pous (genitive podos) "foot" (see foot (n.)). Change of -d- to -l- in Latin ("Sabine -l-") parallels that in odor/olfactory; see lachrymose.
Sense extended 1848 to "one who controls a balloon," and 1907 to "one who flies an airplane." As an adjective, 1788 as "pertaining to a pilot;" from 1928 as "serving as a prototype." Thus the noun pilot meaning "pilot episode" (etc.), attested from 1962. Pilot light is from 1890.