What is the meaning of trill?

noun

• A note that alternates rapidly with another note a semitone above it.
  • synonyms: shake
• The articulation of a consonant (especially the consonant `r') with a rapid flutter of the tongue against the palate or uvula.
  • usage: "he pronounced his R's with a distinct trill"

verb

• Pronounce with a trill, of the phoneme `r'.
  • usage: "Some speakers trill their r's"
• Sing or play with trills, alternating with the half note above or below.
  • synonyms: warble, quaver