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Webster 1913 Edition

Noun.

The act or habit of talking idly or rapidly, or of making inarticulate sounds; the sounds so made; noise made by the collision of the teeth; chatter.

ppr.

Uttering rapid, indistinct sounds, as birds; talking idly; moving rapidly and clashing, as the teeth.

Noun.

Rapid, inarticulate sounds, as of birds; idle talk; rapid striking of the teeth, as in chilliness.

chattering

chattering ‎(plural chatterings)

A noise that chatters.
- 2007 August 14, Ingfei Chen, “The Beam of Light That Flips a Switch That Turns on the Brain”, in New York Times:
  That speed mimics the natural electrical chatterings of the brain, said Dr. Karl Deisseroth, an assistant professor of bioengineering at Stanford.
Output fluctuation before reaching a stable condition.