Lewis & Short

offensācŭlum, i, n. [offenso], a striking against, a tripping, stumbling (postclass.).

  1. I. Lit.: crebris offensaculis contusa crura, App. M. 9, p. 221, 3.
  2. II. Transf., the object against which one stumbles, a stumbling-block: lapis ecce nostro fixus offensaculo est, Prud. Apoth. 45; so, adversarius nostris offensacula pedibus latenter opponit, Lact. Opt. D. 1.