Lewis & Short

mōmentārĭus, a, um, adj. [momentum],

  1. I. brief, of brief duration, momentary; quick (postclass.): maritus, i. e. who stays but a short time, App. M. 5, p. 164, 21: vita, id. ib. 2, p. 127, 24: cura, Dig. 34, 1, 8.
  2. II. Transf., instantaneous: venenum, that operates quickly, App. M. 10, p. 281, 7.