The Collaborative International Dictionary of English v.0.48:
Oscillate \Os"cil*late\ ([o^]s"s[i^]l*l[=a]t), v. i. [imp. & p.
p. Oscillated ([o^]s"s[i^]l*l[=a]`t[e^]d); p. pr. & vb. n.
Oscillating ([o^]s"s[i^]l*l[=a]`t[i^]ng).] [L. oscillare to
swing, fr. oscillum a swing, a little mask or puppet made to
be hung from trees and swing in the wind, prob. orig., a
little mouth, a dim. from os mouth. See Oral, and cf.
1. To move backward and forward; to vibrate like a pendulum;
to swing; to sway.
2. To vary or fluctuate between fixed limits; to act or move
in a fickle or fluctuating manner; to change repeatedly,
back and forth.
The amount of superior families oscillates rather
than changes, that is, it fluctuates within fixed
limits. --De Quincey.