1861 (adv.), 1870 (n.), "tremulous effect in music," from Italian vibrato, from Latin vibratus, past participle of vibrare "to vibrate" (from PIE root *weip- "to turn, vacillate, tremble ecstatically").

Strictly, the vibrato is distinct from the tremolo, in that the latter involves a perceptible variation in pitch; but in common usage the terms are made synonymous. [Century Dictionary]

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Definitions of vibrato from WordNet

vibrato (n.)
(music) a pulsating effect in an instrumental or vocal tone produced by slight and rapid variations in pitch;