Source : Webster's Revised Unabridged Dictionary (1913)

Trill \Trill\, v. i. [OE. trillen to roll, turn round; of Scand.
   origin; cf. Sw. trilla to roll, Dan. trilde, Icel.
   [thorn]yrla to whirl, and E. thrill. Cf. {Thrill}.]
   To flow in a small stream, or in drops rapidly succeeding
   each other; to trickle. --Sir W. Scott.

         And now and then an ample tear trilled down Her
         delicate cheek.                          --Shak.

         Whispered sounds Of waters, trilling from the riven
         stone.                                   --Glover.

Trill \Trill\, v. t. [OE. trillen; cf. Sw. trilla to roll.]
   To turn round; to twirl. [Obs.] --Gascoigne.

         Bid him descend and trill another pin.   --Chaucer.

Trill \Trill\, v. t. [imp. & p. p. {Trilled}; p. pr. & vb. n.
   {Trilling}.] [It. trillare; probably of imitative origin.]
   To impart the quality of a trill to; to utter as, or with, a
   trill; as, to trill the r; to trill a note.

         The sober-suited songstress trills her lay. --Thomson.

Trill \Trill\, v. i.
   To utter trills or a trill; to play or sing in tremulous
   vibrations of sound; to have a trembling sound; to quaver.

         To judge of trilling notes and tripping feet. --Dryden.

Trill \Trill\, n. [It. trillo, fr. trillare. See {Trill} to
   shake.]
   1. A sound, of consonantal character, made with a rapid
      succession of partial or entire intermissions, by the
      vibration of some one part of the organs in the mouth --
      tongue, uvula, epiglottis, or lip -- against another part;
      as, the r is a trill in most languages.

   2. The action of the organs in producing such sounds; as, to
      give a trill to the tongue. d

   3. (Mus.) A shake or quaver of the voice in singing, or of
      the sound of an instrument, produced by the rapid
      alternation of two contiguous tones of the scale; as, to
      give a trill on the high C. See {Shake}.

Source : WordNet®

trill
     n : a note that alternates rapidly with another note a semitone
         above it [syn: {shake}]
     v 1: pronounce with a trill, of the phoneme `r'; "Some speakers
          trill their r's"
     2: sing or play with trills, alternating with the half note
        above or below [syn: {warble}, {quaver}]