Lewis Short
(adjective) : rĭgŭus, a, um, rigo (perh. not ante-Aug.).
* Act., that waters, irrigates;watering, irrigating: in vallibus amnes,Verg. G. 2, 485.
* Pass., watered, wellwatered: hortus,Ov. M. 8, 646; 10, 190; 13, 797: pratum,Col. 2, 16, 3: mons scatebris fontium,Plin. 5, 1, 1, § 6.—Transf.: quae plurimo lacte rigua bos est,i. e. distended with milk,Sol. 2.— Hence, subst.: rĭgŭa, ōrum, n., well-watered places: circa Babylonis rigua,Plin. 9, 57, 83, § 175; 17, 26, 39, § 247; so once in sing.: rĭgŭus, i, m. (sc. ager), a well-watered place, id. 17, 26, 41, § 250.
Charlton T. Lewis, Charles Short, A Latin Dictionary