1. 1. Consisting of interconnected or interwoven parts; composite.
   2. Composed of two or more units: a complex carbohydrate.
2. Involved or intricate, as in structure; complicated.
3. Grammar.
   1. Consisting of at least one bound form. Used of a word.
   2. Consisting of an independent clause and at least one other independent or dependent clause. Used of a sentence.

1. A whole composed of interconnected or interwoven parts: a complex of cities and suburbs; the military-industrial complex.
2. In psychology, a group of related, often repressed ideas and impulses that compel characteristic or habitual patterns of thought, feelings, and behavior. No longer in scientific use.
3. An exaggerated or obsessive concern or fear.
4. Medicine. The combination of factors, symptoms, or signs of a disease or disorder that forms a syndrome.

[Latin complexus, past participle of complectī, to entwine. See complect.]

SYNONYMS   complex, complicated, intricate, involved, tangled, knotty. These adjectives mean having parts so interconnected as to make the whole perplexing. Complex implies a combination of many associated parts: The composer transformed a simple folk tune into a complex set of variations. Complicated stresses elaborate relationship of parts: The party's complicated platform confused many voters. Intricate refers to a pattern of intertwining parts that is difficult to follow or analyze: "No one could soar into a more intricate labyrinth of refined phraseology" (Anthony Trollope). Involved stresses confusion arising from the commingling of parts and the consequent difficulty of separating them: The movie's plot was criticized as being too involved. Tangled strongly suggests the random twisting of many parts: "Oh, what a tangled web we weave,/When first we practice to deceive!" (Sir Walter Scott). Knotty stresses intellectual complexity leading to difficulty of solution or comprehension: Even the professor couldn't clarify the knotty point.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.