n. & v.
--n.
1. a quavering or vibratory sound, esp. a rapid alternation of sung or played notes.
2 a bird's warbling sound.
3 the pronunciation of r with a vibration of the tongue.
--v.
1. intr. produce a trill.
2 tr. warble (a song) or pronounce (r etc.) with a trill.
Etymology: It. trillo (n.), trillare (v.)