English Reference
noun

radiation

n.
US /ˌɹeɪdiˈeɪʃən/ UK /ɹˌeɪdɪˈeɪʃən/ ra·di·a·tion UK spelling radiations

  1. 01 B2 Upper Intermediate Science

    energy that moves through the air or space, like heat from a fire or light from the sun.

    the process in which energy is emitted as particles or waves, including electromagnetic radiation such as light and radio waves.

    Simple

    The sun's radiation provides the heat and light that plants need to grow.

    In context

    Thermal radiation allows heat to be transferred across a vacuum, which is why we can feel the warmth of the sun despite the empty space between us.

  2. 02 B2 Upper Intermediate Medicine

    dangerous energy produced by nuclear materials or X-ray machines.

    ionising radiation emitted by radioactive substances or high-energy equipment, often associated with health risks or medical treatments.

    Simple

    The workers wore special suits to protect themselves from radiation at the power plant.

    In context

    The patient underwent a course of targeted radiation to shrink the tumour before the surgical team attempted to remove it.

    Usage

    Often used as an uncountable noun when referring to the general phenomenon of radioactivity.

  3. 03 C2 Proficiency AcademicTechnical Science

    the process where one type of animal or plant quickly develops into many new species.

    the rapid diversification of a lineage into several new forms that fill different ecological niches.

    Simple

    The radiation of finches on the islands led to many different beak shapes.

    In context

    The fossil record provides clear evidence of a massive mammalian radiation following the extinction of the dinosaurs at the end of the Cretaceous period.

    Usage

    Commonly appears in the phrase 'adaptive radiation'.

That process produced X-ray radiation along with a powerful "wind" of gas.

ScienceDaily· 16 Aug 2026

Levels of UV radiation vary throughout the day.

BBC News· 22 Jun 2026

Borrowed from Latin radiatio, radiationis. By surface analysis, radiate + -ion.

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

This entry
Origin Latin radiatio
Level B2 · Upper Intermediate
Frequency Common
Updated