English Reference
noun

complexity

n.
US /kəmˈpɫɛksəti/ UK /kəmplˈɛksɪti/ com·plex·i·ty UK spelling complexities

  1. 01 B2 Upper Intermediate Academic

    the quality of having many different parts that are connected in a difficult way.

    the abstract state or quality of being intricate, multifaceted, or difficult to analyse. Uncountable in this general sense.

    Simple

    The complexity of the new tax laws makes them very hard for most people to follow.

    In context

    The sheer complexity of the global supply chain means that a single disruption in one port can affect prices worldwide.

    Usage

    Often used with the preposition 'of' followed by a noun phrase.

  2. 02 C1 Advanced AcademicFormal

    a specific part of something that is difficult to deal with or understand.

    a specific intricate detail or complication within a larger system. Countable in this sense.

    Simple

    We need to consider all the complexities of the situation before we make a final decision.

    In context

    The legal team spent months navigating the complexities of the international merger to ensure full compliance with local regulations.

    Usage

    Frequently used in the plural form 'complexities' to refer to various difficult aspects of a topic.

Usage add complexity · increase complexity · increased complexity

Hysteroscopies are common procedures – classed by the NHS as “high volume low complexity”.

The Guardian· 16 Aug 2026

If we couldn’t make generalisations, we would be paralysed by the world’s complexity.

Aeon· 10 Aug 2026

From complex + -ity. Partially displaced native English manifoldness.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Level C1 · Advanced
Frequency Common
Updated