Source : Webster's Revised Unabridged Dictionary (1913)

Uniformitarian \U`ni*form`i*ta"ri*an\, a. (Geol.)
   Of, pertaining to, or designating, the view or doctrine that
   existing causes, acting in the same manner and with
   essentially the same intensity as at the present time, are
   sufficient to account for all geological changes.

Uniformitarian \U`ni*form`i*ta"ri*an\, n. (Geol.)
   One who accepts uniformitarianism, or the uniformitarian
   doctrine.