Moving very rapidly to and fro or up and down.

Roget 149: changeable, changeful; changing etc. 140; mutable, variable, checkered, ever changing; protean, proteiform^†; versatile.    unstaid^†, inconstant; unsteady, unstable, unfixed, unsettled; fluctuating etc. v.; restless; agitated etc. 315; erratic, fickle; irresolute etc. 605; capricious etc. 608; touch and go; inconsonant, fitful, spasmodic; vibratory; vagrant, wayward; desultory; afloat; alternating; alterable, plastic, mobile; transient etc. 111; wavering.    ... show more

Roget 314: oscillating etc. v.; oscillatory, undulatory, pulsatory^†, libratory, rectilinear; vibratory, vibratile^†; pendulous.