ETYM Italian trillo, from trillare. Related to Trill to shake.
A note that alternates rapidly with another note a semitone above it; SYN. shake.
In music, a rapid oscillation between adjacent notes, also called a shake, exploited both for impressionistic effect, as in the opening bars of Bartók’s Piano Concerto No 3 1945, or to create dramatic tension and ambiguity, as at end of a solo cadenza in a concerto.

To pronounce with a trill, of the phoneme