Lewis & Short

cŏëmptĭo, ōnis, f. [coëmo], jurid. t. t.

  1. I. A pretended purchase of an estate which was subjected to a mock sale for the purpose of divesting it of the burden of certain sacrifices attached to it, Cic. Mur. 12, 27 Moeb.
  2. II. Esp., a marriage, consisting in a mutual mock sale of the parties, by which the wife was freed from the tutela legitima and the family sacra, Gai Inst. 1, 110; 1, 113 sq.; Cic. Fl. 34, 84; id. de Or. 1, 56, 237; Varr. L. L. 6, § 43; cf. id. ap. Non. p. 531, 10 sq.; Serv. ad Verg. G. 1, 31; id. A. 4, 103 (but acc. to Lachm. ad Lucr. 2, 1061 = 2. comptus, q. v.).