Entry 2 senses · 2 variants Webster, 1913 Irritancy · Ir·ri·tan·cy · IPA n. n. 01 n. The state or quality of being null and void; invalidity; forfeiture. 1. The state or quality of being null and void; invalidity; forfeiture.(Scots Law) 02 n. The state or quality of being irritant or irritating. 1. The state or quality of being irritant or irritating.