The Collaborative International Dictionary of English v.0.48:

Irritancy \Ir"ri*tan*cy\, n. [From 1st Irritant.] (Scots Law)
   The state or quality of being null and void; invalidity;
   forfeiture. --Burrill.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Irritancy \Ir"ri*tan*cy\, n. [From 2d Irritant.]
   The state or quality of being irritant or irritating.
   [1913 Webster]