Lewis & Short

Sējus or Sēius, i, m.,

  1. I. a Roman name, Varr. R. R. 3, 2, 7; 3, 2, 11 sq.; Cic. Planc. 5, 12; id. Off. 2, 17, 58; Tac. A. 2, 20; 4, 1; 6, 7 al.
    Hence,
  2. II. Sējānus, a, um, adj., of or belonging to Sejus, Sejan: aedes, Varr. R. R. 3, 2, 7 fin.: pastiones, id. ib. 3, 2, 7, § 12: equus, the horse of a certain Cn. Sejus, that brought misfortune to him and to all subsequent possessors: hinc proverbium de hominibus calamitosis ortum dicique solitum: ille homo habet equum Sejanum, Gell. 3, 9, 6.
    1. B. Subst.: L. Aelius Sejanus, son of Sejus Strabo, the powerful praefectus praetorii of Tiberius, Tac. A. 4, 1 sq.; Tib. 55 sq.
      Hence, Sējānĭānus, a, um, adj., of or pertaining to L. Ælius Sejanus: satellites, Sen. Cons. ad Marc. 1, 2: Sejanianum jugum, id. ib. 1, 3.