complex

The word “complex” means made up of many interconnected parts; not simple. In plain terms, complicated and made of many connected parts, or (as a noun) a set of buildings or a set of emotional hang-ups.

“Complex” is pronounced KOMP-lehks (/kɑmˈplɛks/ in IPA).

Here is “complex” used in a sentence: “The negotiations involved a complex web of political interests.”

Words with a similar meaning to “complex” include complexed, complicate, complicated, convoluted, Gordian and involute.

The opposite of “complex” — its antonyms — are incomplex, noncomplex, noncomplicated, simple and simplex.

Depending on how it is used, “complex” can be an adjective and a noun.

The word “complex” comes from Latin. From Latin complexus, past participle of complector, "to entwine or encircle," from com- ("together") plus plectere ("to weave" or "braid").

“Complex” is a very common word in modern English, usually learned at around the B1 level.

Both mean not simple, but there is a useful distinction. "Complex" describes something with many interconnected parts that can still be understood, like a machine or an ecosystem. "Complicated" suggests something confusing or tangled that is hard to follow. Complexity is about structure; complication is about difficulty. A system can be complex without being complicated.

The most direct opposite is "simple," meaning made of few parts and easy to understand. Other antonyms include "straightforward," "basic," "plain," and "uncomplicated." Which fits best depends on context: a simple design, a straightforward task, or a basic structure all contrast with something complex in slightly different ways.

The human body is a classic example, with organs, nerves, and chemical systems all interacting. Other examples include a global supply chain, a legal case with many parties, or software built from thousands of connected components. In each, no single part explains the whole — the interaction between parts creates the complexity.

Complex is largely neutral and descriptive. It can be positive, praising rich, sophisticated flavour or thinking, or negative, hinting that something is hard to manage. The tone depends on context: "a complex character" sounds admiring, while "this got complex" often signals frustration. The word itself simply notes many interacting parts.