Lewis & Short

lūsōrĭus, a, um, adj. [lusor], of or belonging to a player.

  1. I. Lit.: pila, a playing-ball, Plin. 7, 56, 57, § 205: alveus cum tesseris, id. 37, 2, 6, § 13.
    Hence,
      1. 2. Subst.: lūsōrĭum, ii, n., a place where shows of gladiators and wild beasts were given: statuit sibi triclinium in summo lusorio, Lampr. Heliog. 25; Lact. Mort. Persecut. 21.
    1. B. Used for pleasure; hence, as subst.: lūsōrĭa, ae, f. (sc. navis), a vessel for pleasure, yacht, Sen. Ben. 7, 20, 3; and, transf., any kind of light vessel, cutter: lusoriis navibus discurrere flumen ultro citroque, with cruisers, Amm. 17, 2, 3.
      Plur.: lusoriae, swift-sailing cruisers, cutters, Vop. Bonos. 15: de lusoriis Danubii, Cod. Th. 7, tit. 17.
  2. II. Trop.
    1. A. That serves for amusement or pastime, sportive: quaestio, Plin. 7, 53, 54, § 180: arma, Sen. Ep. 117, 25: spectaculum non fidele et lusorium, id. ib. 80, 2.
    2. B. Transf., that is done or given in play; hence, empty, ineffectual, invalid, = irritus: nomen, Sen. Ben. 5, 8, 3: lusorias minas alicui facere, Dig. 35, 3, 4: imperium, ib. 43, 8, 1.
      Hence, adv.: lūsōrĭē, playfully, in sport, not in earnest, apparently: lusorie (causam) agens, Dig. 30, 1, 50, § 1.