\Ir"ri*tant\, a. [LL. irritants, -antis, p. pr. of
irritare to make null, fr. L. irritus void; pref. ir- not +
ratus established.] (Scots Law)
Rendering null and void; conditionally invalidating.
      The states elected Harry, Duke of Anjou, for their
      king, with this clause irritant; that, if he did
      violate any part of his oath, the people should owe him
      no allegiance.                           --Hayward.

\Ir"ri*tant\, a. [L. irritans, -antis, p. pr. of
irritare: cf. F. irritant. See {Irritate} to excite.]
Irritating; producing irritation or inflammation.

\Ir"ri*tant\, n. [Cf. F. irritant.]
1. That which irritates or excites.
2. (Physiol. & Med.) Any agent by which irritation is
   produced; as, a chemical irritant; a mechanical or
   electrical irritant.
3. (Toxicology) A poison that produces inflammation.
{Counter irritant}. See under {Counter}.
{Pure irritant} (Toxicology), a poison that produces
   inflammation without any corrosive action upon the
   tissues.