quaver
— Verb
– English
~ give off unsteady sounds, alternating in amplitude or frequency
quaver
— Verb
– English
~ sing or play with trills, alternating with the half note above or below
quavering
— Adjective
– English
~ (of the voice) quivering as from weakness or fear; "the old lady's quavering voice"; "spoke timidly in a tremulous voice"
quaveringly
— Adverb
– English
~ in an unsteady quavering manner; "the man began quaveringly to question the soldier"