\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.