Merriam-Webster Collegiate Dictionary - trill

 I. verb  Etymology: Middle English; akin to Middle Dutch ~en to vibrate, Swedish ~a to roll  Date: 14th century  intransitive verb  1. to flow in a small stream or in drops ; trickle  2. twirl, revolve  transitive verb to cause to flow in a small stream  II. noun  Etymology: Italian ~o probably of imitative origin  Date: 1649  1.  a. the alternation of two musical tones a diatonic second apart — called also shake  b. vibrato  c. a rapid reiteration of the same tone especially on a percussion instrument  2. a sound resembling a musical ~ ; warble  3.  a. the rapid vibration of one speech organ against another (as of the tip of the tongue against the teethridge)  b. a speech sound made by a ~  III. verb  Date: circa 1667  intransitive verb to play or sing with a ~ ; quaver  transitive verb to utter as or with or as if with a ~ ~ the r  • ~er noun