1 An organized structure made up of interconnected units.
2 In psychoanalysis, an organized collection of ideas, emotions, impulses, and memories that share a common emotional tone and that have been excluded either partly or entirely from consciousness but continue to influence a person's thoughts, emotions, and behaviour. This concept was introduced in 1895 by the Austrian physician Josef Breuer (1842–1925) in Studies on Hysteria (Standard Edition, II, at p. 231) and later adapted by Sigmund Freud (1856–1939) and Carl Gustav Jung (1875–1961). The word complex is derived from complexion (2) in the transitional sense already established by the time of Shakespeare's Hamlet: ‘So oft it chances in particular men, / That for some vicious mole of nature in them, / As in their birth, wherein they are not guilty / (Since nature cannot choose his origin), / By the o'ergrowth of some complexion, / Oft breaking down the pales and forts of reason … ’ (I.iv.23–8). See castration complex, complex indicator, Diana complex, Electra complex, father complex, inferiority complex, inverted Oedipus complex, Jocasta complex, mother complex, Oedipus complex, Orestes complex, particular complex, Phaedra complex, word-association test.
3 In informal usage, an obsession or a phobia. Compare complexion (2). [From Latin com- together + plexus plaited or twined, from plectere to braid]