The Collaborative International Dictionary of English v.0.48:

Clique \Clique\ (kl[=e]k), n. [F., fr. OF. cliquer to click. See
   Click, v. i.]
   A narrow circle of persons associated by common interests or
   for the accomplishment of a common purpose; -- generally used
   in a bad sense.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Clique \Clique\, v. i.
   To To associate together in a clannish way; to act with
   others secretly to gain a desired end; to plot; -- used with
   together.
   [1913 Webster]

WordNet (r) 3.0 (2006):

clique
    n 1: an exclusive circle of people with a common purpose [syn:
         clique, coterie, ingroup, inner circle, pack,
         camp]

Moby Thesaurus II by Grady Ward, 1.0:

93 Moby Thesaurus words for "clique":
   age group, associate with, assort with, band, battalion, bevy,
   body, brigade, bunch, cabal, cadre, camarilla, camp, cast, cell,
   charmed circle, chum, chum together, chum with, circle, clan,
   clique with, closed circle, club together, cohort, company,
   complement, consort with, contingent, corps, coterie, covey, crew,
   crowd, detachment, detail, division, elite, elite group, faction,
   fellowship, fleet, flock together, fraternize, gang, group,
   grouping, groupment, hang around with, hang out with,
   herd together, hobnob with, in-group, ingroup, inner circle, join,
   join in fellowship, junta, junto, keep company with, mingle with,
   mix with, mob, movement, out-group, outfit, pack, pal, pal up with,
   pal with, party, peer group, phalanx, platoon, posse, regiment,
   ring, run in couples, run with, salon, set, sort with, squad,
   stable, string, take up with, team, tie up with, tribe, troop,
   troupe, we-group, wing



The Free On-line Dictionary of Computing (30 December 2018):

clique

    A maximal totally connected subgraph.
   Given a graph with nodes N, a clique C is a subset of N
   where every node in C is directly connected to every other
   node in C (i.e. C is totally connected), and C contains all
   such nodes (C is maximal).  In other words, a clique contains
   all, and only, those nodes which are directly connected to all
   other nodes in the clique.

   [Is this correct?]

   (1996-09-22)