Source : Webster's Revised Unabridged Dictionary (1913)

Inirritable \In*ir"ri*ta*ble\, a. [Pref. in- not + irritable:
   cf. F. inirritable.]
   Not irritable; esp. (Physiol.), incapable of being stimulated
   to action, as a muscle. -- {In*ir`ri*ta*bil"i*ty}, n.