Lewis & Short

dēcursĭo, ōnis, f. [decurro], a running or flowing down (less freq. than decursus; not in Cic.).

  1. I. In gen.: aquae, Arn. 2, p. 84.
  2. II. In partic., milit. t. t., a manœuvre, military exercise, evolution, a descent, hostile attack, Brutus ap. Cic. Fam. 11, 10, 4; Hirt. B. G. 8, 24, 3; Auct. B. Alex. 42.
    Hence,
    1. B. Transf., a walking or running in complete armor at a solemnity or for exercise, Suet. Calig. 18; id. Galb. 6.