Lewis & Short

2. ductus, ūs, m. [duco], a leading, conducting (class.).

  1. I. Lit.
    1. A. In gen.: aquarum, Cic. Off. 2, 4, 14; id. Leg. 2, 1, 2; cf. the work of Frontinus: De aquaeductibus; in this sense also simply ductus, id. ib. 5 sq.: aequali ductu porticus, a line, row, Lucr. 4, 426: muri, Cic. Rep. 2, 6, 11: litterarum, form, shape, Quint. 1, 1, 25; 10, 2, 2; Plin. 8, 3, 3, § 6: oris (with vultus), lineaments, Cic. Fin. 5, 17, 47: liniarum, Plin. 37, 12, 74, § 195.
    2. B. In partic., military lead, conduct, generalship, command, Cic. de Imp. Pomp. 21; id. Fam. 3, 11, 4; Caes. B. G. 7, 62, 2; id. B. C. 1, 7, 6; Vell. 2, 78; 115; Tac. Agr. 5; Suet. Vesp. 4 al.; freq. connected with auspicium, Plaut. Am. 1, 1, 41; Liv. 5, 46; 8, 31; 28, 38; Inscr. Orell. 563 al.; sometimes also opp. to auspicium, as the supreme command, Tac. A. 2, 41; Curt. 6, 3; Suet. Aug. 21 Ruhnk.
  2. II. Trop., of discourse.
    1. A. Connection, structure of a play, Quint. 4, 2, 53.
    2. B. A period, Quint. 9, 4, 30 Spald.