Lewis & Short

2. ortus, ūs, m. [orior].

  1. I. A rising of the heavenly bodies (opp. occasus; class.): solis et lunae reliquorumque siderum ortus, obitus motusque cognoscere, Cic. Div. 1, 56, 128: primi sub lumina solis et ortus, Verg. A. 6, 255: (sol) ab ortu ad occasum commeans, from east to west, Cic. N. D. 2, 19, 49: solis, sunrise, i. e. the orient, the east, id. Cat. 3, 8: tum bis ad occasum, bis se convertit ad ortus, Ov. M. 14, 386: nitido ab ortu, id. ib. 2, 112: signorum, Verg. E. 9, 46: ortus lucis, Vulg. Sap. 16, 28.
  2. II. A rise, beginning, origin (cf. origo): tribuniciae potestatis, Cic. Leg. 3, 8, 19: juris, id. ib. 1, 6, 20: Favonii, Plin. 17, 9, 8, § 57: materno ortu, Ov. M. 13, 148: ab Elide ducimus ortum, we are sprung, derive our origin, id. ib. 5, 494: ortus nascentium, the birth, Cic. Div. 2, 43, 91; id. Tusc. 1, 38, 91: Cato ortu Tusculanus, by birth, id. Leg. 2, 2, 5.
    Of a river, the source: donec venias ad fluminis ortus, Ov. M. 11, 139.
    Of plants, the springing up, growth, Lucr. 5, 211.