Lewis & Short

sŏcer (nom. socerus, Plaut. Cas. 4, 2, 18; id. Men. 5, 5, 54; with socer, id. ib. 5, 7, 56), ĕri, m. [Gr. ἑκυρός].

  1. I. A father-in-law, Plaut. Stich. 4, 1, 22; id. Trin. 5, 2, 27; Cic. Off. 1, 35, 129; id. Lael. 1, 1 and 5; Caes. B. G. 1, 12 fin.; Ov. M. 1, 145; Hor. C. 3, 11, 39; id. Ep. 1, 19, 30 al.; v. also socrus.
    Plur. soceri, parents-in-law, Verg. A. 2, 457; 10, 79; Ov. M. 3, 132.
  2. II. Transf., for consocer, a son’s father-in-law, Ter. Hec. 5, 2, 4: magnus, grandfather-in-law, i. e. one’s husband’s or wife’s grandfather, Dig. 38, 10, 4, § 6; called simply socer, ib. 50, 16, 146; cf. ib. 3, 1, 3; 23, 2, 14 fin.: socer major, a great-grandfather-in-law, Paul. Diac. p. 136, 10.