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]

The Free On-line Dictionary of Computing (19 January 2023):

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)