# complex

/ˈkɑmpɫɛks/ (US)

Source: https://englishreference.com/word/complex
Updated: 2026-06-19

## Senses

### 1. complicated

adjective · CEFR B1

having many different parts and being difficult to understand.

For teachers: consisting of many interconnected parts; intricate or complicated in structure.

- The instructions for the new software were too complex for me to follow.
- The legal team spent months untangling the complex web of financial transactions that led to the company's collapse.

### 2. mathematical numbers

adjective · CEFR C1 · Technical

related to a type of number that has both a real part and an imaginary part.

For teachers: pertaining to numbers of the form a + bi, where i is the square root of negative one.

- We learned how to plot complex numbers on a graph today.
- The engineer used complex variables to model the fluid dynamics of the turbine blades under high pressure.

### 3. group of buildings

noun · CEFR B2

a group of buildings or rooms that are close together and used for a similar purpose.

For teachers: a whole structure or connected series of buildings or facilities.

- The new sports complex has a swimming pool and three gyms.
- The industrial complex on the edge of the city houses several manufacturing plants and a central distribution warehouse.

### 4. psychological issue

noun · CEFR B2

a group of feelings or worries that influence how someone behaves, often without them knowing it.

For teachers: a related group of repressed mental networks that dominate a person's emotional life.

- He has a bit of a superiority complex and always thinks he is right.
- Psychologists suggest that her childhood experiences contributed to an inferiority complex that manifests in her professional life.

### 5. chemical structure

noun · CEFR C1 · Technical

a structure where a central atom is connected to other molecules.

For teachers: a molecular entity formed by the loose association of two or more component molecules or ions.

- The scientist studied how the protein complex reacts to the new medicine.
- The stability of the metal-ligand complex is highly dependent on the pH levels of the surrounding solution.

### 6. to join together

verb · CEFR C2 · Technical

to join with another substance to form a single structure.

For teachers: to form a complex with another substance; often used in biochemical contexts.

- The dye will complex with the fibers to create a permanent color.
- The researchers observed the metal ions as they began to complex with the organic molecules in the sample.

## Examples

- The new sports complex has three swimming pools.
- The company is moving its headquarters to a massive office complex outside the city center.
- Architects designed the residential complex to integrate seamlessly with the surrounding parkland, ensuring that the structural density did not overwhelm the natural landscape.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.