Lewis & Short

sīdo, sīdi, 3, v. n. [cf. sedeo; Gr. ἵζω], to seat one’s self, sit down; to settle, alight (poet. and in post-Aug. prose; usu. of things)

  1. I. In gen.: quaesitisque diu terris, ubi sidere detur, Ov. M. 1, 307; cf.: (columbae) super arbore sidunt, Verg. A. 6, 203: canes sidentes, sitting down, Plin. 10, 63, 83, § 177.
        1. b. Of things, to sink down, settle: sidebant campi (shortly after: subsidere saxa), Lucr. 5, 493: nec membris incussam sidere cretam, id. 3, 382; cf. Col. 12, 24, 2: in tepidā aquā gutta (balsami) sidens ad ima vasa, Plin. 12, 25, 54, § 123: cummi in aquā sidit, id. 12, 25, 54, § 121: cave lecticā sidat, be set down, Prop. 4 (5), 8, 78: prius caelum sidet inferius mari, Quam, etc., Hor. Epod. 5, 79.
  2. II. In partic., pregn.
    1. A. To sit or be set fast; to remain sitting, lying, or fixed: mare certis canalibus ita profundum, ut nullae ancorae sidant, can hold, Plin. 6, 22, 24, § 82: secures sidunt, id. 16, 10, 19, § 47: tum queror, in toto non sidere pallia lecto, remain lying, Prop. 4 (5), 3, 31.
      1. 2. Naut. t. t., of a vessel, to stick fast on shallows: veniat mea litore navis Servata, an mediis sidat onusta vadis, Prop. 3, 14 (3, 6), 30; cf.: ubi eae (cymbae) siderent, Liv. 26, 45; Quint. 12, 10, 37; Tac. A. 1, 70; 2, 6; Nep. Chabr. 4, 2.
    2. B. To sink down, to sink out of sight.
      1. 1. Lit.: non flebo in cineres arcem sidisse paternos Cadmi, Prop. 3, 9 (4, 8), 37: sidentes in tabem spectat acervos, settling or melting down, Luc. 7, 791; cf. Stat. S. 5, 3, 199.
      2. 2. Trop.: vitia civitatis pessum suā mole sidentis, sinking, Sen. Const. 2; cf.: sidentia imperii fundamenta, Plin. 15, 18, 20, § 78: sidente paulatim metu, Tac. H. 2, 15.