complex, a.

  1. Consisting of or comprehending various parts united or connected together; formed by combination of different elements; composite, compound. Said of things, ideas, etc. (Opposed to simple, both here and in sense 2.)

   2. esp.    a. Consisting of parts or elements not simply co-ordinated, but some of them involved in various degrees of subordination; complicated, involved, intricate; not easily analysed or disentangled.

complex, n.

   1. a. A whole comprehending in its compass a number of parts, esp. (in later use) of interconnected parts or involved particulars; a complex or complicated whole.

   {dag}2. An interweaving, contexture. Obs.

   3. Psychol. A group of emotionally charged ideas or mental factors, unconsciously associated by the individual with a particular subject, arising from repressed instincts, fears, or desires and often resulting in mental abnormality; freq. with defining word prefixed, as inferiority, {Oe}dipus complex, etc.; hence colloq., in vague use, a fixed mental tendency or obsession. Also attrib. and Comb.

Source: Oxford English Dictionary (Online Ed.)