trill

(noun) a note that alternates rapidly with another note a semitone above it. Synonyms: shake.

(noun) the articulation of a consonant (especially the consonant `r') with a rapid flutter of the tongue against the palate or uvula. Example: "He pronounced his r's with a distinct trill."

(verb) pronounce with a trill, of the phoneme `r'. Example: "Some speakers trill their r's."

(verb) sing or play with trills, alternating with the half note above or below. Synonyms: warble, quaver.