Lewis & Short

merso, āvi, ātum, 1, v. freq. a. [mergo], to dip in, immerse (poet. and in post-Aug. prose).

  1. I. Lit.: balantumque gregem fluvio mersare salubri, Verg. G. 1, 272: balneo infertur, calida aqua mersatur, Tac. A. 15, 69.
  2. II. Trop., to overwhelm: rerum copia mersat, drowns, destroys, Lucr. 5, 1008: mersor civilibus undis, plunge myself, Hor. Ep. 1, 1, 16.
  3. III. Pass.: mersari, to set, of the stars, Mart. Cap. 8, § 844; cf. merto.