Lewis & Short

Ĕleusin, īnis (acc. Eleusin, Front. Strat. 4, 7, 44; Lat. form Eleusina, ae, Front. Ep. ad Ver. 1, p. 178; Cl. Mam. Grat. Act. Jul. 9, 3; Oros. 1, 7; and acc. to MSS. Eleusinam in Cic. N. D. 1, 42, 119; Liv. 31, 25, 2; cf. Salaminam from Salamis, q. v.), f., = Ἐλευσίν,

  1. I. a very ancient city of Attica, famous for its mysteries of Ceres, now Lepsina, Plin. 4, 7, 11, § 23; Cic. Att. 6, 6, 2; id. N. D. 1, 42, 119; Liv. 31, 26; Tac. H. 4, 83; Ov. F. 4, 507; id. M. 7, 439; Stat. Th. 2, 382 al.
  2. II. Hence,
    1. A. Ĕleusīnus, a, um, adj., Eleusinian: mater, i. e. Ceres, Verg. G. 1, 163; cf.: Eleusina Ceres et Proserpina, Vitr. 7 praef. fin.; Lact. 1, 21, 24; Arn. 6, no. 6; Serv. Verg. A. 4, 99.
    2. B. Ĕleusī-nĭus, a, um, adj., = Ἐλευσίνιος, Eleusinian: sacra, Suet. Claud. 25; Gell. 11, 6, 5; cf.: Eleusinium certamen, id. 15, 20, 3.
      Subst.: Ĕleusīnĭa, ōrum, n., the festival of Ceres at Eleusin, Tert. Apol. 7; id. adv. Val. 1.