complex

American  

[kuhm-pleks, kom-pleks, kom-pleks] / kəmˈplɛks, ˈkɒm plɛks, ˈkɒm plɛks /

adjective

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.

   Antonyms:

   simple

3. so complicated or intricate as to be hard to understand or deal with.

   a complex problem.

   Synonyms:

   labyrinthine, tangled, knotty

   Antonyms:

   simple

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.

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noun

complexes plural

1. an intricate or complicated association or assemblage of related things, parts, units, etc..

   the entire complex of our educational system; an apartment complex.

   Synonyms:

   labyrinth, tangle, web, network

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.

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.

complex British  

/ ˈkɒmplɛks /

adjective

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

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noun

1. a whole made up of interconnected or related parts

   a 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 fear

   he'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

Usage

Complex is sometimes wrongly used where complicated is meant. Complex is properly used to say only that something consists of several parts. It should not be used to say that, because something consists of many parts, it is difficult to understand or analyse

Other Word Forms

Derived Forms

• complexness
  noun
• uncomplexness
  noun
• overcomplex
  adjective
• quasi-complex
  adjective
• supercomplex
  adjective
• uncomplex
  adjective
• complexly
  adverb
• quasi-complexly
  adverb
• uncomplexly
  adverb

Inflected Forms

Nouns

• complexes
  plural

Etymology

Origin of complex

First recorded in 1645–55; 1905–10 complex for def. 7; adjective from Latin complexus, past participle of complectī, complectere “to embrace, encompass, include,” equivalent to complect- ( see complect) + -tus past participle suffix; noun from Late Latin complexus “totality, complex” ( Latin: “inclusion, grasping, embrace”), equivalent to complect(ere) + -tus suffix of verb action; reanalysis of the Latin verb as “to intertwine (completely)” influenced sense of the adjective

Explanation

People who are really good at math can handle complex math problems. The rest of us are all set with simple stuff like the times tables. Use complex to refer to something that is not simple. Something complex has two or more related parts, or is not simple in its structure. As a noun, a complex is a group of units, often a group of buildings. The adjective is stressed on the second syllable, but the noun is stressed on the first syllable. Complex is from Latin complexus, from complecti "to encircle or embrace."

Example Sentences

See Examples For:

complex complexes

By 2000, Congress had eliminated both, citing concerns that the restrictions were complex to administer and could stifle savings or penalize successful investment.

From The Wall Street Journal ● Jul. 22, 2026

However, they say "significant hotspots remain across a large and complex landscape" and crews will stay at the scene until the incident is brought to a safe conclusion.

From BBC ● Jul. 21, 2026

The first phase of construction will include installing the massive LED screen planned to wrap around the base of the complex at 11th, Figueroa and 12th streets.

From Los Angeles Times ● Jul. 21, 2026

Most drones, which are assembled from a series of sometimes off-the-shelf components, are both smaller and less complex to make.

From The Wall Street Journal ● Jul. 21, 2026

It easily rolled over the plant’s 30-foot seawall, sweeping a tractor trailer into the building complex and pulling a massive oil tank into the ocean when it receded.

From "Meltdown" by Deirdre Langeland

About 17 million gallons of water ripped through parked cars and flooded apartment complexes.

From Los Angeles Times ● Jul. 18, 2026

But due to much of this World Cup using existing stadia, hotels, training complexes and travel infrastructure, "there won't be any economic benefits from development".

From BBC ● Jul. 16, 2026

Videos and posts circulating online show international fans reacting to oversized portions, large-format retail stores, and highway travel stops that feel closer to entertainment complexes than convenience stores.

From Salon ● Jun. 28, 2026

One 11,000-hectare area along the Red River -- roughly the size of Paris -- is slated to become a warren of high-end residential complexes and parks, with roughly 250,000 residents relocated.

From Barron's ● Jun. 24, 2026

Today I could not find my way around its newly built freeways, its thriving industrial complexes, its racially mixed, upscale suburban sprawl.

From "Warriors Don't Cry: A Searing Memoir of the Battle to Integrate Little Rock's Central High" by Melba Pattillo Beals

Related Words

• complicated
• convoluted
• disturbing
• intricate
• obscure
• perplexing
• sophisticated