Tremulant

The night air wrapped them warmly, and the balm of the little breezes that stirred the foliage around them was the smell of damask roses from the garden. . . . She stood by the bench, one hand resting on it; she stood all in the tremulant shadow.

Lightning exploded through the sky, followed quickly by a tremulant clap of thunder.

[S]he continued in a throaty, yet tremulant voice, punctuating her words with a shy, small smile.

The tremulant is a small apparatus that gives to the tone of any department of an organ to which it may be applied a waving or undulating effect.

The tremulant intentionally disturbs the stability of the wind in order to produce a desirable musical oscillation.