complex

1 of 3

noun

com·​plex ˈkäm-ˌpleks 

1

: a whole made up of complicated or interrelated parts

a complex of welfare programs

the military-industrial complex

2

a

: a group of culture traits relating to a single activity (such as hunting), process (such as use of flint), or culture unit

b(1)

: a group of repressed desires and memories that exerts a dominating influence upon the personality

a guilt complex

(2)

: an exaggerated reaction to or preoccupation with a subject or situation

He has always had a complex about spiders.

She has a weight complex.

Not being able to find a job was giving me a complex.

c

: a group of obviously related units of which the degree and nature of the relationship is imperfectly known

d

: the sum of factors (such as symptoms) characterizing a disease or condition

primary tuberculous complex

3

: a chemical association of two or more species (such as ions or molecules) joined usually by weak electrostatic bonds rather than covalent bonds

4

: a building or group of buildings housing related units

an apartment complex

a sports complex

complex

2 of 3

adjective

com·​plex käm-ˈpleks 

kəm-ˈpleks,

ˈkäm-ˌpleks

1

a

: composed of two or more parts : composite

a complex mixture of chemicals

b(1)

of a word : having a bound form as one or more of its immediate constituents

Unmanly is a complex word.

(2)

of a sentence : consisting of a main clause and one or more subordinate clauses

2

: hard to separate, analyze, or solve

a complex problem

3

: of, concerned with, being, or containing complex numbers

a complex root

complex analysis

complexly adverb

complexness noun

complex

3 of 3

verb

com·​plex käm-ˈpleks 

kəm-ˈpleks,

ˈkäm-ˌpleks

complexed; complexing; complexes

transitive verb

1

: to make complex or into a complex

2

: chelate

complexation

ˌkäm-ˌplek-ˈsā-shən 

kəm-

noun

Did you know?

The Complex Origins of Complex

The word complex lives up to its name, as it contains multiple parts of speech and senses. It serves as an adjective, a noun, and, less commonly, as a verb. The verb use is the oldest of the three, with an original meaning of “to join or unite.” Complex comes from the Latin complecti, which means “to entwine around, to embrace,” a word that is based in part on plectere (“to braid”). English has a number of other words that can be traced to plectere, including perplex, plexus (“an intricately interwoven combination of elements or parts in a cohering structure”), and amplexus (“the mating embrace of some amphibians, such as frogs and toads”).

Synonyms

Noun

• facility

Adjective

• complicated
• intricate
• complicate
• sophisticated

Verb

• complicate

Choose the Right Synonym for complex

complex, complicated, intricate, involved, knotty mean having confusingly interrelated parts.

complex suggests the unavoidable result of a necessary combining and does not imply a fault or failure.

a complex recipe

complicated applies to what offers great difficulty in understanding, solving, or explaining.

complicated legal procedures

intricate suggests such interlacing of parts as to make it nearly impossible to follow or grasp them separately.

an intricate web of deceit

involved implies extreme complication and often disorder.

a rambling, involved explanation

knotty suggests complication and entanglement that make solution or understanding improbable.

knotty ethical questions

Examples of complex in a Sentence

Noun

She has a complex about her appearance.

a complex of protein molecules

Adjective

The house's wiring is complex.

The situation is more complex than you realize.

Verb

there's no need to complex what should be a simple process for obtaining a building permit

Recent Examples on the Web

Noun

In late April, the Milwaukee County Board of Supervisors passed a resolution formally calling on county officials to ensure access to services at the Milwaukee County Courthouse complex and safeguard individuals' right to due process. —Vanessa Swales, jsonline.com, 27 Oct. 2025

Lund was taken into custody Friday at an apartment complex in Dublin, while Morton, who police say also lived there, was arrested separately at San Francisco International Airport after returning from international travel. —Stepheny Price, FOXNews.com, 27 Oct. 2025

Adjective

This program prepares students to be leaders who are critical, analytical thinkers who know how to understand and respond to today’s complex global threats. —Foreign Affairs, 29 Oct. 2025

This geometric architecture may even explain how complex organisms evolved so rapidly — not by inventing new genes, but by rearranging the ways existing ones are used. —Neetika Walter, Interesting Engineering, 29 Oct. 2025

Word History

Etymology

Noun

borrowed from Latin complexus "embrace, grasp, inclusion" (Late Latin also, "whole, entirety") from complector, complectī "to embrace, grasp, encompass, include" + -tus, suffix of action nouns; (sense 2b (1)) after German Komplex — more at complex entry 2

Adjective

borrowed from Late Latin complexus "composite, connected, intertwined," going back to Latin, past participle of complector, complectī "to embrace, grasp, encompass, include," from com- com- + -plectī, deponent form of plectere "to plait, twine" — more at ply entry 3

Verb

derivative of complex entry 1 or complex entry 2

First Known Use

Noun

circa 1652, in the meaning defined at sense 1

Adjective

circa 1652, in the meaning defined at sense 1a

Verb

1658, in the meaning defined at sense 1

Phrases Containing complex

• AIDS-related complex
• B complex
• complex carbohydrate
• complex fraction
• complex number
• complex plane
• complex regional pain syndrome
• compound-complex
• conjugate complex number
• coordination complex
• Electra complex
• Golgi complex
• inferiority complex
• major histocompatibility complex
• military-industrial complex
• MSG symptom complex
• Napoleon complex
• Oedipus complex
• prison industrial complex
• superiority complex
• synaptinemal complex
• synaptonemal complex
• vitamin B complex
• white savior complex

Kids Definition

complex

1 of 2 noun

com·​plex ˈkäm-ˌpleks 

1

: a whole made up of many complicated or related parts

2

: a system of thoughts, feelings, and memories that exist in one's mind but of which one is not aware and which influence one's behavior

3

: a building or group of buildings housing related units

an apartment complex

complex

2 of 2 adjective

com·​plex käm-ˈpleks 

kəm-;

ˈkäm-ˌpleks

1

a

: composed of two or more parts

a complex mixture

b

: consisting of a main clause and one or more subordinate clauses

a complex sentence

c

: formed by union of simpler substances

2

: having many parts, details, ideas, or functions often related in a complicated way

a complex problem

a complex machine

complexly adverb

Medical Definition

complex

1 of 3 adjective

com·​plex käm-ˈpleks  kəm-ˈ 

ˈkäm-ˌ

1

: having many varied interrelated parts, patterns, or elements and consequently hard to understand

complex behavior

a complex personality

complex plants and animals

2

: formed by the union of simpler chemical substances

complex proteins

complex

2 of 3 noun

com·​plex ˈkäm-ˌpleks 

1

: a group of repressed memories, desires, and ideas that exert a dominant influence on the personality and behavior

a guilt complex

see castration complex, electra complex, inferiority complex, oedipus complex, persecution complex, superiority complex

2

: a group of chromosomes arranged or behaving in a particular way see gene complex

3

: a chemical association of two or more species (as ions or molecules) joined usually by weak electrostatic bonds rather than by covalent bonds

4

: the sum of the factors (as symptoms and lesions) characterizing a disease

primary tuberculous complex

complex

3 of 3 transitive verb

com·​plex käm-ˈpleks  kəm-ˈ 

ˈkäm-ˌ

1

: to form into a complex

RNA complexed with protein

2

: chelate

intransitive verb

: to form a complex

hormones which must complex with specific receptors