quaver: [15] Quaver was derived from an earlier and now obsolete Middle English quave ‘tremble’. This was of Germanic origin (Low German has the related quabbeln ‘tremble’), and probably started life as a vocal realization of the action of trembling. The use of the noun quaver for a short musical note (first recorded in the 16th century) comes from the original singing of such notes with a trill.
quaver (v.)
"to vibrate, tremble," early 15c., probably a frequentative of cwavien "to tremble, shake" (early 13c.), which probably is related to Low German quabbeln "tremble," and possibly of imitative origin. Meaning "sing in trills or quavers" first recorded 1530s. Related: Quavered; quavering.
quaver (n.)
1560s, in music, "eighth note," from quaver (v.). Meaning "a tremble in the voice" is from 1748.