trem·o·lo 
(trĕmə-lō′)
(trĕmə-lō′)n. pl. trem·o·los
1. A tremulous effect produced by rapid repetition of a single tone or by rapid alternation of two tones.
2. A device on an organ for producing a tremulous effect.
3. Vibrato, especially in singing.
[Italian, from Latin tremulus, tremulous; see TREMULOUS.]