Source : Webster's Revised Unabridged Dictionary (1913)

Momentary \Mo"men*ta*ry\, a. [L. momentarius. See {Moment}.]
   Done in a moment; continuing only a moment; lasting a very
   short time; as, a momentary pang.

         This momentary joy breeds months of pain. --Shak.

Source : WordNet®

momentary
     adj : lasting for a markedly brief time; "a fleeting glance";
           "fugitive hours"; "rapid momentaneous association of
           things that meet and pass"; "a momentary glimpse" [syn:
            {fleeting}, {fugitive}, {momentaneous}]