English Reference
adjective · noun

radical

adj. · n.
US /ˈɹædəkəɫ/ UK /ɹˈædɪkəl/ rad·i·cal UK spelling radicals

  1. 01 B2 Upper Intermediate

    adj.describing a very big or important change that affects the basic nature of something.

    adj.relating to or affecting the fundamental nature of something; far-reaching or thoroughgoing.

    Simple

    The company needs a radical change in how it treats its customers.

    In context

    The new CEO proposed a radical restructuring of the entire organization to eliminate redundant management layers.

  2. 02 C1 Advanced Academic

    adj.supporting complete social or political change.

    adj.advocating for thorough or complete social and political reform from the roots up.

    Simple

    He joined a radical political group while he was at university.

    In context

    The manifesto outlined a radical vision for wealth redistribution that alienated the more moderate members of the party.

  3. 03 C1 Advanced Formal

    n.someone who wants to change the whole social or political system.

    n.a person who advocates for thorough or complete social and political reform.

    Simple

    In the 1960s, many students were seen as radicals by the government.

    In context

    The historian argued that the radicals of the nineteenth century paved the way for modern democratic institutions.

  4. 04 C2 Proficiency Technical Science

    n.a group of atoms that usually stays together during a chemical reaction.

    n.an atom, molecule, or ion that has at least one unpaired valence electron and is often highly reactive.

    Simple

    Antioxidants help protect your body from damage caused by free radicals.

    In context

    The researcher monitored the formation of short-lived radicals during the combustion process using high-speed spectroscopy.

    free radical
  5. 05 C1 Advanced Technical

    n.the part of a Chinese character that often shows its general meaning.

    n.the graphical component of a Chinese character under which the character is traditionally listed in a dictionary.

    Simple

    The radical for 'water' appears on the left side of many characters related to liquid.

    In context

    Students of Mandarin often find that memorizing the 214 traditional radicals significantly accelerates their ability to recognize complex characters.

    componentclassifier
  6. 06 C2 Proficiency Technical Math

    n.a sign used to show the root of a number, like a square root.

    n.a quantity expressed as a root of another quantity; also the symbol used to denote such a root.

    Simple

    You need to simplify the expression under the radical.

    In context

    The equation requires the extraction of a cubic radical to find the value of the unknown variable.

Usage radical attack · radical challenge

And on Broadway, Cats: The Jellicle Ball , a heartbreakingly brilliant interpretation of the original show in which a tired-seeming vehicle, badly damaged by the terrible film version, gets a radical makeover.

The Guardian· 14 Aug 2026

That’s why hearing reproductive education discussed in the context of aiding women’s self-understanding, wellbeing and mental health feels so radical.

The Guardian· 12 Aug 2026

PIE word *wréh₂ds Inherited from Middle English radical, from Latin rādīcālis (“of or pertaining to the root, having roots, radical”). Compare grassroots.

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

This entry
Origin Latin rādīcālis
Level C1 · Advanced
Frequency Common
Updated