Lewis & Short

commentātĭo, ōnis, f. [commentarius].

  1. I. Abstr., a diligent meditation upon something, a studying, a careful preparation, μελέτη (so perh. only in Cic.): loci multa commentatione atque meditatione parati, Cic. de Or. 2, 27, 118.
    In plur., Cic. de Or. 1, 60, 257; id. Brut. 71, 249; 27, 105: commentatio inclusa in veritatis lucem proferenda est, id. de Or. 1, 34, 157.
      1. * 2. As rhet. fig., = ἐνθύμημα, Quint. 5, 10, 1.
    1. B. Trop.: tota philosophorum vita, ut ait idem (Socrates), commentatio mortis est, Cic. Tusc. 1, 30, 74 (transl. of Plat. Phaed. § 12: Τὸ μελέτημα αὐτὸ τοῦτό ἐστι τῶν φιλοσόφων, λύσις καὶ χωρισμὸς Ψυχῆς ἀπὸ σώματος), commentatio ferendi doloris, id. ib. 2, 18, 42.
  2. II. Concr., a learned work, treatise, dissertation, description (so perh. not ante-Aug.): commentatio (de naturā animalium), Plin. 8, 16, 17, § 44; so, Indiae, id. 6, 17, 21, § 60.
    In plur., Plin. 28, 1, 2, § 7; Gell. praef. § 4.