Lewis & Short

orsa, ōrum, n. [ordior].

  1. I. Beginnings, commencements, an undertaking, attempt: ut (di) orsis tanti operis successus prosperos darent, Liv. praef. fin.: Orsa juvare, Val. Fl. 1, 21.
  2. II. In partic., words, speech (poet.): sic orsa vicissim Ore refert, Verg. A. 7, 435; 10, 632; 11, 124; Val. Fl. 5, 472: Menandri, i. e. carmina, Aus. Idyll. 4, 46.