English Reference
noun

diffusion

n.
US /dɪfˈjuʒən/ UK /dɪfjˈuːʒən/ dif·fu·sion UK spelling diffusions

  1. 01 C1 Advanced Technical Science

    the way gas or liquid molecules spread out and mix together naturally.

    the net movement of molecules or atoms from a region of high concentration to a region of low concentration as a result of random thermal motion.

    Simple

    The diffusion of the perfume meant that soon the whole room smelled like roses.

    In context

    In biological systems, the diffusion of oxygen across cell membranes is a fundamental process for maintaining cellular respiration.

    Usage

    Often used with the preposition 'of'.

  2. 02 C1 Advanced Academic

    the way that new ideas, languages, or customs spread from one group of people to another.

    the process by which cultural traits, social institutions, or linguistic practices spread from one society or community to another.

    Simple

    The diffusion of Greek culture across the ancient world changed how people lived.

    In context

    Sociologists study the diffusion of innovations to understand how new technologies are adopted by different segments of the population.

    Usage

    Commonly appears in the phrase 'cultural diffusion'.

  3. 03 C1 Advanced Technical Science

    the way light spreads out when it hits a rough surface or passes through something like a cloud.

    the scattering of light by reflection from a rough surface or by transmission through a translucent medium.

    Simple

    The diffusion of sunlight through the thick curtains made the room feel soft and warm.

    In context

    Photographers often use a screen to encourage the diffusion of light, which helps to eliminate harsh shadows on the subject's face.

Once inside the joint, therapeutic compounds are released through diffusion and gradual relaxation of the hydrogel matrix.

ScienceDaily· 31 Aug 2026

At room temperature, phonons generally scatter more frequently and quickly lose the coherence needed for wave-based transport, causing heat to spread through ordinary diffusion.

ScienceDaily· 7 Aug 2026

Borrowed from Latin diffūsiō, from diffundō; can be decomposed as diffuse + -ion.

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

This entry
Origin Latin diffūsiō
Level C1 · Advanced
Frequency Frequent
Updated