Lewis & Short

dĕorsum (dissyll. per synaeresin, Lucr. 1, 362; 2, 205 al.; cf., on the contrary, trisyll., id. 2, 202.
Also deorsus, like prorsus, quorsus, rursus, adversus, Cic. N. D. 1, 25, 69; Ap. M. 8, p. 207, 18; id. ib. 9, p. 236, 40; id. de Deo Socr. p. 47, 35; id. Flor. no. 15), adv. [contr. from devorsum, turned down], downwards, κάτω, opp. to sursum (class.).

  1. I. To indicate motion: ego me deorsum duco de arbore, Plaut. Aul. 4, 8, 8: deorsum cuncta feruntur (opp. flammae expressae sursum), Lucr. 2, 202; 205; 6, 335; Cic. N. D. 1, 25, 69; id. Fin. 1, 6, 18; Cels. 5, 26, 31: reliqui (gestus) ante nos et dextra laevaque et sursum et deorsum aliquid ostendunt, Quint. 11, 3, 105: deorsum cadit, Plaut. Rud. 1, 2, 89; cf.: ut isto gladio deorsus ad meum Tlepolemum viam quaeram, i. e. in orcum, Ap. M. 8, p. 207, 18.
        1. b. Pleonast. with versus (versum): ubi deorsum versus ibit, Cato R. R. 156, 4; Varr. R. R. 2, 7, 5; Quadrig. ap. Gell. 9, 1, 1: ubi eo veneris, clivos deorsum vorsum est, right down before you, Ter. Ad. 4, 2, 35.
        2. c. With sursum, up and down, ἄνω κάτω: ne sursum deorsum cursites, Ter. Eun. 2, 2, 47; cf.: naturis sursum deorsum, ultro citro commeantibus, Cic. N. D. 2, 33, 84: si sanguis sursum deorsumve erupit, Cels. 2, 8: cum terra quatitur et sursum ac deorsum movetur, Sen. Q. N. 6, 21.
  2. II. To indicate position, locality, down, below: qui colunt deorsum, magis aestate laborant: qui sursum, magis hieme … nec non sursum quam deorsum tardius seruntur ac metuntur, Varr. R. R. 1, 6, 3; Plaut. Aul. 2, 7, 5; Ter. Ad. 4, 2, 34 sq.; Vulg. Deut. 4, 39 al.
    Cf. on this art. Hand, Turs. II. p. 280- 282.