c.1330 (intrans.) "to be thrilled or tingling," of uncertain origin, possibly a frequentative form of
tick (2) in its older sense of "to touch." The OE form was
tinclian. Some suggest a metathesis of
kittle (M.E.
kytyllen), from Du.
kietelen, from a common North Sea Gmc. word for "to tickle" (cf. O.N.
kitla, O.H.G.
kizzilon, Ger.
kitzeln). Meaning "to excite agreeably" (c.1386) is a translation of L.
titillare. Meaning "to touch lightly so as to cause a peculiar and uneasy sensation" is recorded from 1398; that of "to poke or touch so as to excite laughter" is from 1423; fig. sense of "to excite, amuse" is attested from 1688. The noun is recorded from 1801.
Ticklish in the lit. sense of "easily tickled" is recorded from 1598, later than the fig. sense (1581); an earlier word for this was
tickly (1530).
Tickled "pleased, happy" is from 1586.