irritanta.[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.)a.[L. irritans, -antis, p. pr. of irritare: cf. F. irritant. See Irritate to excite.] Irritating; producing irritation or inflammation.()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.()