Source : Webster's Revised Unabridged Dictionary (1913)

Irritably \Ir"ri*ta*bly\, adv.
   In an irritable manner.

Source : WordNet®

irritably
     adv 1: in a petulant manner; "he said testily; `Go away!'" [syn: {testily},
             {petulantly}, {pettishly}]
     2: in an irritable manner; "she had become irritably exact"