Definition of "Trill" :

noun: a note that alternates rapidly with another note a semitone above it

noun: the articulation of a consonant (especially the consonant r') with a rapid flutter of the tongue against the palate or uvula

"He pronounced his R's with a distinct trill."

verb: sing or play with trills, alternating with the half note above or below

verb: pronounce with a trill, of the phoneme r'

"Some speakers trill their r's."