quaver

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To quiver, as from weakness; tremble.
• intransitive verb To speak in a quivering voice; utter a quivering sound.
• intransitive verb Music To produce a trill on an instrument or with the voice.
• intransitive verb To utter or sing in a trilling voice.
• noun A quivering sound.
• noun A trill.
• noun An eighth note.

from The Century Dictionary.

• To have a tremulous motion; tremble; vibrate.
• To sing or sound with the wavy tones of an untrained voice, or with a distinctly tremulous tone; hence, to sing, in general; also, to perform a shake or similar melodic embellishment with the voice or an instrument.
• To sing in an artless manner or with tremulous tone.
• noun A quivering; a trembling.
• noun A tremulous or quivering sound or tone.
• noun A shake or similar embellishment, particularly in vocal music.
• noun An eighth-note (which see).

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To utter with quavers.
• intransitive verb To tremble; to vibrate; to shake.
• intransitive verb Especially, to shake the voice; to utter or form sound with rapid or tremulous vibrations, as in singing; also, to trill on a musical instrument.
• noun A shake, or rapid and tremulous vibration, of the voice, or of an instrument of music.
• noun (Mus.) An eighth note. See Eighth.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a trembling shake.
• noun a trembling of the voice, as in speaking or singing.
• noun music an eighth note, drawn as a crotchet (quarter note) with a tail.
• verb to shake in a trembling manner.
• verb to use the voice in a trembling manner, as in speaking or singing.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a tremulous sound
• verb give off unsteady sounds, alternating in amplitude or frequency
• verb sing or play with trills, alternating with the half note above or below
• noun a musical note having the time value of an eighth of a whole note