Lewis & Short

expŏsĭtĭo, ōnis, f. [expono].

  1. I. An exposing of an infant (post-class.), Justin. 1, 4, 9; 1, 5, 4.
  2. II. Of speech.
    1. A. A setting forth, exposition, an exhibiting, showing; a narration: cursum contentiones magis requirunt; expositiones rerum tarditatem, Cic. Or. 63, 212; Auct. Her. 1, 10, 17; 1, 3, 4; 2, 2, 3; Cic. de Or. 3, 53, 203; Quint. 4, 1, 35; 4, 2, 2 et saep.
    2. B. A definition, explanation: duplices summi boni, Cic. Fin. 5, 8, 21 (cf. exponere, id. ib. § 22 Madv.; and 5, 5, 14, p. 635).