English Reference
noun

reactor

n.
US /ɹiˈæktɝ/ UK /ɹɪˈæktɐ/ re·ac·tor UK spelling reactor's, reactor's

  1. 01 B2 Upper Intermediate Science

    a large machine that uses nuclear energy to create heat and electricity.

    an apparatus in which a nuclear chain reaction is initiated, sustained, and controlled to generate heat or produce useful isotopes.

    Simple

    The power plant has three reactors that provide electricity for the whole city.

    In context

    Engineers monitored the core temperature of the nuclear reactor to ensure the cooling systems were functioning within safety parameters.

    nuclear pileatomic pile
  2. 02 C1 Advanced Technical Chemistry

    a container used in a factory to hold and control chemical reactions.

    a vessel designed for carrying out a chemical reaction, often equipped with mechanisms for temperature and pressure control.

    Simple

    The chemicals are mixed inside a large steel reactor to create the plastic.

    In context

    The industrial reactor was lined with glass to prevent the acidic reactants from corroding the outer steel shell during the synthesis process.

  3. 03 C2 Proficiency Technical Computing

    a part in an electrical system that resists changes in current.

    an electrical device, such as an inductor, used primarily to introduce reactance into a circuit.

    Simple

    The technician replaced the faulty reactor in the power supply unit.

    In context

    Current-limiting reactors are installed in the substation to protect the electrical grid from the high currents generated during a short circuit.

    inductorchoke
  4. 04 C2 Proficiency Formal

    someone who responds to a situation or a suggestion.

    an individual who responds to a specific stimulus, influence, or suggestion.

    Simple

    He is a slow reactor and needs time to think before he answers.

    In context

    Psychological studies often categorise participants as either fast or slow reactors based on their immediate physiological responses to stress.

The Almaraz plant in the western region of Extremadura was slated to close in 2028 as part of the government's plan to shut all nuclear reactors by 2035 and bet heavily on renewables.

The Local· 14 Aug 2026

The drought-hit Danube, whose waters cool the Romanian plant in Cernavoda, already forced Nucelarelectrica to shut down ⁠one reactor ​in late July.

The Guardian· 14 Aug 2026

From react + -or.

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

This entry
Level B2 · Upper Intermediate
Frequency Frequent
Updated