Lewis & Short

neptis, is, f. (like nepos, orig. comm.; as masc., still found in an inscr.: C. COELIO VERO NEPTI, Inscr. Murat. 692, 2; cf. nepos as fem. in class. Lat. exclusively) [1. nepos], a granddaughter: filii, filiae, nepotes, neptes, Cic. Tusc. 1, 35, 85: neptes Licinias, id. Brut. 58, 211: vestis ab uxore et filiā, neptibusque confecta, Suet. Aug. 73; 31: neptis Veneris, i. e. Ino, Ov. M. 4, 530: doctas Cybeleia, neptes vidit, i. e. the Muses, id. F. 4, 191; Juv. 6, 265.
Acc.: neptim, Curt. 6, 2, 7.
Abl.: nepti, Tac. A. 3, 24.
Gen. plur.: neptium, Just. Inst. 3, 1, 15 Krüg.
Also, a niece, Spart. Hadr. 2; cf. 1, nepos init.