Lewis & Short

sŏcĭus, a, um, adj. [root sec- of sequor],

  1. I. sharing, joining in, partaking, united, associated, kindred, allied, fellow (mostly poet. and in post-Aug. prose; cf. subst. infra): hic (Augustus) socium cum Jove nomen habet, Ov. F. 1, 608: aurea possedit socio Capitolia templo Mater, i. e. in common with Jupiter, id. ib. 6, 73: regnum, id. M. 5, 378: classis, id. ib. 13, 352: sepulcrum, id. H. 11, 123: lectus, id. A. A. 2, 377: ignes, id. M. 9, 795: anni, id. H. 2, 33: linguae, id. Tr. 5, 10, 35: dei, id. F. 2, 618: spes, id. M. 13, 375: sociis quid noctibus uxor anxia, Stat. S. 3, 5, 1: platanus clara in Lyciā gelidi fontis sociā amoenitate, Plin. 12, 1, 5, § 9: potestas, Amm. 26, 2, 8.
  2. II. Esp., leagued, allied, confederate: cura sociae retinendae urbis, Liv. 27, 1; so, urbs, id. 31, 24: civitates, id. 41, 6 fin.; Quint. 3, 8, 12; cf.: civitas nobis, Tac. A. 13, 57: agmina, Verg. A. 2, 371: manus, i. e. of the allies (in the Bellum Sociale), Ov. Am. 3, 15, 10: classis, id. M. 13, 352: arma, Sil. 7, 635.
    Hence, substt
    1. A. sŏcĭus, i, m. (gen. plur. socium, Liv. 43, 6, 12; 44, 21, 10; v. II. B. infra; also in the poets, Verg. A. 5, 174; Prop. 3, 7, 41; Neue, Formenl. 1, 112 sq.).
      1. 1. In gen., fellow, sharer, partner, comrade, companion, associate (very freq. and class.; syn.: consors, particeps): belli particeps et socius et adjutor, Cic. Att. 9, 10, 5; cf.: consiliorum omnium particeps et socius paene regni, id. Rep. 2, 20, 35; cf.: regni sociis, Luc. 1, 92: hereditatis, Plin. Pan. 38: tuorum consiliorum (with particeps), Plaut. Mil. 4, 2, 22: fortunarum omnium (with particeps), Cic. Font. 17, 37 (21, 47): me quidem certe tuarum actionum, sententiarum, rerum denique omnium socium comitemque habebis, id. Fam. 1, 9, 22: praeter Laelium neminem habeo culpae socium, id. Att. 11, 14, 1: Agusius, omnium laborum, periculorum meorum socius, id. Fam. 13, 71: socius et consors gloriosi laboris, id. Brut. 1, 2; Sall. J. 29, 2: Romuli socius in Sabino proelio, Cic. Rep. 2, 8, 14; for which, with dat.: alicui socius, Plaut. Rud. 1, 2, 72: hunc cape consiliis socium, Verg. A. 5, 712: hos castris adhibe socios, id. 8, 56: socium esse in negotiis, Ter. Heaut. 3, 1, 9: quia sine sociis nemo quicquam tale conatur, Cic. Lael. 12, 42: socium ad malam rem quaerere, Plaut. As. 2, 2, 22: cum sociis operum, Hor. Ep. 2, 1, 142: ante alios Infert se socium Aeneas, Verg. A. 4, 142: amissā sociorum parte, Ov. M. 14, 242.
        Poet.: generis socii, i. e. relatives, Ov. M. 3, 259; cf. sanguinis, id. Tr. 4, 5, 29: tori, i. e. a spouse, consort, id. M. 14, 678.
      2. 2. In partic.
        1. a. In mercant. lang., a copartner, partner in business: socii putandi sunt, quos inter res communicata est, etc., Cic. Verr. 2, 3, 20, § 50; id. Rosc. Am. 40, 116; id. Quint. 3, 12: nefarium est socium fallere qui se in negotio conjunxit, id. Rosc. Com. 6, 16.
          So, socii, of the company of farmers of the public revenue, Cic. Fam. 13, 9, 3; Plin. 33, 7, 40, § 120; cf. societas, II. A. 2.
          Hence,
          1. (β) Jurid. t. t.: pro socio (agere, damnari, etc.), for defrauding a partner, Cic. Fl. 18, 43; id. Quint. 3, 13; cf. Dig. 17, tit. 2: Pro socio.
        2. b. In publicists’ lang., an ally, confederate (cf. foederatus); plur., Plaut. Men. 1, 2, 25: servate vestros socios, id. Cist. 1, 3, 51: Boios receptos ad se socios sibi asciscunt, Caes. B. G. 1, 5 fin.; 1, 11 fin.; 1, 14; 1, 15; 1, 36: Cyprius rex, cujus majores huic populo socii atque amici semper fuerunt, Cic. Dom. 20, 52; Liv. 29, 17; 44, 1 et saep. al.; opp. hostes, Sall. C. 51, 38; id. J. 92, 2.
          Sing.: socius et amicus populi Romani, Sall. J. 24, 3.
          In the connection, socii et Latini, or, more freq., socii et nomen Latinum, the term socii denotes the Italian people dwelling out of Latium who were under the protection of and allied with Rome, the Italian allies, Cic. Lael. 3, 12; id. Rep. 6, 12, 12; id. Sest. 13, 30; id. Rep. 1, 19, 31; 3, 29, 41; Sall. J. 39, 2; 42, 1: socii nomenque Latinum, id. ib. 43, 4 Kritz N. cr.; Liv. 29, 27; for which, also: socii ac nominis Latini, id. 41, 8; and without ellipsis: per homines nominis Latini et socios Italicos impedimenta parabant, Sall. J. 40, 2; cf. also: quos (milites) uti ex Latio et a sociis cogeret, id. ib. 95, 1.
          The socii Latini nominis, on the other hand, are simply the Latin allies, the Latins, Liv. 40, 36; 32, 8; 41, 12: socii ab nomine Latino, id. 22, 38.
          In this sense the gen. plur. is usually socium, Liv. 21, 17, 2; 22, 27, 11 et saep.: socii navales, id. 21, 50; v. navalis.
    2. B. sŏcĭa, ae, f.: eos, qui nos socias sumpserunt sibi, Plaut. Stich. 1, 2, 45: (eloquentia) pacis est comes otiique socia, Cic. Brut. 12, 45: vitae socia virtus, mortis comes gloria, id. Font. 17, 39 (21, 49); cf.: est socia mortis homini vita ingloria, Publ. Syr. App. 213 Rib.: nox socia, Cic. Phil. 2, 18, 45: quam plurimas uxores habent. … nulla pro sociā obtinet, Sall. J. 80, 7: addit se sociam, Verg. E. 6, 20: socias sorores Impietatis habet, Ov. M. 4, 3: hic socias tu quoque junge moras, id. A. A. 1, 492: sociae doloris casusque tui, App. M. 5, p. 166, 18.
      Poet.: socia generisque torique, related by blood and marriage, relative and wife (Juno), Ov. M. 1, 620; so, tori, id. ib. 8, 521; 10, 268: ulmus cum sociā vite, id. ib. 14, 662.