Source : Webster's Revised Unabridged Dictionary (1913)

Tickle \Tic"kle\, v. t. [imp. & p. p. {Tickled}; p. pr. & vb. n.
   {Tickling}.] [Perhaps freq. of tick to beat; pat; but cf.
   also AS. citelian to tickle, D. kittelen, G. kitzlen, OHG.
   chizzil[=o]n, chuzzil[=o]n, Icel. kitla. Cf. {Kittle}, v. t.]
   1. To touch lightly, so as to produce a peculiar thrilling
      sensation, which commonly causes laughter, and a kind of
      spasm which become dengerous if too long protracted.

            If you tickle us, do we not laugh?    --Shak.

   2. To please; to gratify; to make joyous.

            Pleased with a rattle, tickled with a straw. --Pope.

            Such a nature Tickled with good success, disdains
            the shadow Which he treads on at noon. --Shak.

Source : WordNet®

tickling
     adj : exciting by touching lightly so as to cause laughter or
           twitching movements [syn: {tingling}, {titillating}]
     n : the act of tickling [syn: {tickle}, {titillation}]