The Collaborative International Dictionary of English v.0.48:

Clan \Clan\ (kl[a^]n), n. [Gael. clann offspring, descendants;
   akin to Ir. clann, cland, offspring, tribe, family; perh.
   from L. plania scion, slip, cutting. Cf. Plant, n.]
   1. A tribe or collection of families, united under a
      chieftain, regarded as having the same common ancestor,
      and bearing the same surname; as, the clan of Macdonald.
      "I have marshaled my clan." --Campbell.
      [1913 Webster]

   2. A clique; a sect, society, or body of persons; esp., a
      body of persons united by some common interest or pursuit;
      -- sometimes used contemptuously.
      [1913 Webster]

            Partidge and the rest of his clan may hoot me.
                                                  --Smolett.
      [1913 Webster]

            The whole clan of the enlightened among us. --Burke.
      [1913 Webster]

WordNet (r) 3.0 (2006):

clan
    n 1: group of people related by blood or marriage [syn: kin,
         kin group, kinship group, kindred, clan, tribe]