Processionary \Pro*ces"sion*a*ry\, a. [Cf. LL. processionarius, F. processionnaire.] Pertaining to a procession; consisting in processions; as, processionary service. {Processionary moth} (Zo["o]l.), any moth of the genus {Cnethocampa}, especially {C. processionea} of Europe, whose larv[ae] make large webs on oak trees, and go out to feed in regular order. They are covered with stinging hairs.