How do you spell Irritant

Available Definitions:
1)  a. - Rendering null and void; conditionally invalidating.
2)  a. - Irritating; producing irritation or inflammation.
3)  n. - That which irritates or excites.
4)  n. - Any agent by which irritation is produced; as, a chemical irritant; a mechanical or electrical irritant.
5)  n. - A poison that produces inflammation.