The Collaborative International Dictionary of English v.0.48:
Quaver \Qua"ver\, v. i. [imp. & p. p. Quavered; p. pr. & vb.
n. Quavering.] [OE. quaven to shake, to tremble; cf. LG.
quabbeln to shake, to be soft, of fat substances, quabbe a
fat lump of flesh, a dewlap, D. kwabbe, and E. quiver, v.]
1. To tremble; to vibrate; to shake. --Sir I. Newton.
2. 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