The main complex meaning is made of many parts that are connected to each other, so that the whole thing is difficult to understand or deal with. A complex problem has lots of moving pieces, and changing one piece affects the others.
Complex is also a noun: a group of buildings used together (a sports complex), a strong emotional pattern in psychology (a guilt complex), and a technical term in chemistry. Grammar adds one more use, the complex sentence. Each of these senses gets its own section and examples below, and shows how complex differs from complicated.
Entry at a glance
Meaning
Adjective: having many linked parts; hard to analyse. Noun: a group of related buildings or things; an emotional fixationPart of speech
Adjective and noun (plural: complexes)Pronunciation
KOM-pleks; the adjective is also said kuhm-PLEKSWord forms
complexity (noun), complexly (adverb, rare)Origin
Latin complexus, from complecti, to embrace or encircle; in English from the 17th centuryOpposite
simple, plain, basic, straightforwardClose words
complicated, intricate, involved, elaborate
Complex meaning as an adjective
- Made of many connected parts. The human brain is a complex organ. A complex network of roads.
- Difficult to understand or solve. Tax law is complex. She has complex feelings about moving abroad.
- Rich and layered, used as praise for flavour, music or character: a complex coffee with notes of chocolate and fruit, a complex villain.
Note that complex is not always negative. A complex story or wine can be a compliment; a complex form you have to fill in is usually not.
Complex as a noun
- Group of buildings or facilities. An apartment complex, a shopping complex, a temple complex, the industrial complex near the port.
- Psychology. A group of linked emotions and memories that strongly shapes behaviour, often without the person realising. In everyday speech, an inferiority complex means feeling less worthy than others, and a guilt complex means feeling guilty out of proportion. Saying someone "has a complex about" their height means they are touchy about it. For more on the mind, see psychology.
- Chemistry and biology. A structure formed when molecules or ions join together, such as a protein complex.
Complex sentence definition
In grammar, a complex sentence has one independent clause (it can stand alone as a sentence) and at least one dependent clause (it cannot stand alone). Dependent clauses usually begin with words like because, although, when, if, since, who or which.
- Although it was raining, we went for a walk.
- I'll call you when the train arrives.
- The phone that I bought last month has already cracked.
| Sentence type | Structure | Example |
|---|---|---|
| simple | one independent clause | We left early. |
| compound | two independent clauses joined by and, but, or, so | We left early, but the road was closed. |
| complex | one independent plus one or more dependent | We left early because the road was closed. |
| compound-complex | two or more independent plus at least one dependent | We left early because of the forecast, but we still got wet. |
So to define complex sentence in one line: a main clause with a subordinate clause attached. The words that link them are covered on our conjunction page.
Complex or complicated?
People often treat these as the same, and in casual talk that is fine. Careful writers draw a line:
- Complex means many parts that interact, which you can understand with study. A city's transport system is complex.
- Complicated stresses confusion, hassle or unnecessary difficulty. Assembling cheap furniture with bad instructions is complicated.
A relationship can be either: complex if it has many layers, complicated if it is messy and hard to sort out.
More example sentences
- The heist plan in the novel was so complex that even the robbers lost track of it.
- We rented a flat in a large housing complex with a shared pool.
- Climate is a complex system shaped by oceans, air, ice and living things.
- He developed a complex about his accent after classmates teased him.
- The teacher asked us to rewrite three simple sentences as complex sentences.
Origin of the word
English took complex from French complexe, from Latin complexus, "surrounding, encompassing", the past participle of complecti, "to embrace". That verb was built from com- (together) and plectere (to weave or braid). So at its root, something complex is woven together. The grammar term complex sentence is recorded from the 18th century, and psychologists gave the noun its mental sense around 1907.
Clause types, parts of speech and other sentence terms are collected under grammar and writing.
Frequently asked questions
Complex sentence meaning: how would you explain it simply?
A complex sentence is one main idea that can stand alone plus at least one extra part that cannot, joined by words like because, when or although. Example: I stayed home because I was sick.
Does complex sound good or bad?
That depends. A complex problem sounds tough, but a complex flavour or character is often praise. The context tells you.
How do you pronounce complex?
The noun is always KOM-pleks. The adjective is usually KOM-pleks too, though you will also hear kuhm-PLEKS, with the weight on the end.
What is an inferiority complex?
In everyday speech it means a lasting feeling of being less good than other people, which can make someone shy or defensive. Psychologists use the idea more carefully than casual speakers.
What is the plural of complex?
The plural is complexes, as in two apartment complexes or a cluster of protein complexes.
Is the definition of complex just hard?
Partly. Complex things are often hard, but the core idea is many connected parts. A long hike is hard but not complex; a chess position can be complex without being physically hard.