1. composed of many interconnected parts; compound; composite: a complex highway system.
  2. characterized by a very complicated or involved arrangement of parts, units, etc.: complex machinery.
  3. so complicated or intricate as to be hard to understand or deal with: a complex problem.
  4. Grammar.
    1. (of a word) consisting of two parts, at least one of which is a bound form, as childish, which consists of the word child and the bound form -ish.
    2. complex sentence.
  5. Mathematics. pertaining to or using complex numbers: complex methods; complex vector space.


  1. an intricate or complicated association or assemblage of related things, parts, units, etc.: the entire complex of our educational system; an apartment complex.
  2. Psychology. a system of interrelated, emotion-charged ideas, feelings, memories, and impulses that is usually repressed and that gives rise to abnormal or pathological behavior.
  3. a fixed idea; an obsessive notion.
  4. Mathematics.
    1. an arbitrary set of elements of a group.
    2. a collection of simplexes having specified properties.
  5. Also called coordination compound. Chemistry. a compound in which independently existing molecules or ions of a nonmetal (complexing agent) form coordinate bonds with a metal atom or ion.Compare ligand(def 2).
  6. Biochemistry. an entity composed of molecules in which the constituents maintain much of their chemical identity: receptor-hormone complex, enzyme-substrate complex.

verb (used with object)

  1. Chemistry. to form a complex with.

verb (used without object)

  1. Chemistry. to form a complex.


  1. made up of various interconnected parts; composite
  2. (of thoughts, writing, etc) intricate or involved
  3. grammar
    1. (of a word) containing at least one bound form
    2. (of a noun phrase) containing both a lexical noun and an embedded clause, as for example the italicized parts of the following sentence: I didn’t know the man who served me
    3. (of a sentence) formed by subordination of one clause to another
  4. maths of or involving one or more complex numbers


  1. a whole made up of interconnected or related partsa building complex
  2. psychoanal a group of emotional ideas or impulses that have been banished from the conscious mind but that continue to influence a person’s behaviour
  3. informal an obsession or excessive fearhe’s got a complex about cats
  4. Also called: coordination compound a chemical compound in which molecules, groups, or ions are attached to a central metal atom, esp a transition metal atom, by coordinate bonds
  5. any chemical compound in which one molecule is linked to another by a coordinate bond

1650s, “composed of parts,” from French complexe “complicated, complex, intricate” (17c.), from Latin complexus “surrounding, encompassing,” past participle of complecti “to encircle, embrace,” in transferred use, “to hold fast, master, comprehend,” from com- “with” (see com-) + plectere “to weave, braid, twine, entwine,” from PIE *plek-to-, from root *plek- “to plait” (see ply (v.1)). The meaning “not easily analyzed” is first recorded 1715. Complex sentence is attested from 1881.


1650s, “a whole comprised of parts,” from complex (adj.). Psychological sense of “connected group of repressed ideas” was established by C.G. Jung, 1907.


  1. A group of related, often repressed memories, thoughts, and impulses that compel characteristic or habitual patterns of feelings, thought, and behavior.
  2. The relatively stable combination of two or more ions or compounds into a larger structure without covalent binding.
  3. A composite of chemical or immunological structures.
  4. An entity made up of three or more interrelated components.
  5. A group of individual structures known or believed to be anatomically, embryologically, or physiologically related.
  6. The combination of factors, symptoms, or signs that forms a syndrome.


  1. Consisting of interconnected or interwoven parts; composite.
  2. Composed of two or more units.
  3. Relating to a group of individual structures known or considered to be anatomically, embryologically, or physiologically related.
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