The Collaborative International Dictionary of English v.0.48:

Social \So"cial\, a. [L. socialis, from socius a companion; akin
   to sequi to follow: cf. F. social. See Sue to follow.]
   1. Of or pertaining to society; relating to men living in
      society, or to the public as an aggregate body; as, social
      interest or concerns; social pleasure; social benefits;
      social happiness; social duties. "Social phenomena." --J.
      S. Mill.
      [1913 Webster]

   2. Ready or disposed to mix in friendly converse;
      companionable; sociable; as, a social person.
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   3. Consisting in union or mutual intercourse.
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            Best with thyself accompanied, seek'st not
            Social communication.                 --Milton.
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   4. (Bot.) Naturally growing in groups or masses; -- said of
      many individual plants of the same species.
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   5. (Zool.)
      (a) Living in communities consisting of males, females,
          and neuters, as do ants and most bees.
      (b) Forming compound groups or colonies by budding from
          basal processes or stolons; as, the social ascidians.
          [1913 Webster]

   Social science, the science of all that relates to the
      social condition, the relations and institutions which are
      involved in man's existence and his well-being as a member
      of an organized community; sociology. It concerns itself
      with questions of the public health, education, labor,
      punishment of crime, reformation of criminals, and the
      like.

   Social whale (Zool.), the blackfish.

   The social evil, prostitution.
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   Syn: Sociable; companionable; conversible; friendly;
        familiar; communicative; convival; festive.
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WordNet (r) 3.0 (2006):

social
    adj 1: relating to human society and its members; "social
           institutions"; "societal evolution"; "societal forces";
           "social legislation" [syn: social, societal]
    2: living together or enjoying life in communities or organized
       groups; "a human being is a social animal"; "mature social
       behavior" [ant: unsocial]
    3: relating to or belonging to or characteristic of high
       society; "made fun of her being so social and high-toned"; "a
       social gossip colum"; "the society page"
    4: composed of sociable people or formed for the purpose of
       sociability; "a purely social club"; "the church has a large
       social hall"; "a social director"
    5: tending to move or live together in groups or colonies of the
       same kind; "ants are social insects"
    6: marked by friendly companionship with others; "a social cup
       of coffee"
    n 1: a party of people assembled to promote sociability and
         communal activity [syn: sociable, social, mixer]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "social":
   affable, affair, amiable, amusing, associated, associational,
   at home, civic, civil, clubbable, clubbish, clubby, coalitional,
   collective, collectivistic, common, communal, communicative,
   communistic, community, commutual, companionable, companionate,
   compatible, congenial, conjoint, convivial, cooperative, cordial,
   cosmopolitan, courteous, entertaining, fit for society,
   fond of society, friendly, gathering, general, genial,
   get-together, gracious, gregarious, group, hospitable, in common,
   international, joint, levee, matinee, mutual, national,
   organizational, pleasant, pleasurable, popular, public, reception,
   reciprocal, reunion, salon, sexual, sociable, social affair,
   social gathering, social-minded, socialistic, societal, society,
   soiree, state, supranational, urbane, venereal, wake