Source : Webster's Revised Unabridged Dictionary (1913)

Mordacity \Mor*dac"i*ty\, n. [L. mordacitas: cf. F.
   mordacit['e]. See {Mordacious}.]
   The quality of being mordacious; biting severity, or
   sarcastic quality. --Bacon.

Source : WordNet®

mordacity
     n : a disposition to biting