English Reference
noun

effectiveness

n.
US /ˈifɛktɪvnəs/ UK /ɪfˈɛktɪvnəs/ ef·fec·tive·ness

  1. 01 B2 Upper Intermediate

    how well something works to get the result you planned.

    the quality of being successful in producing a desired or intended result. Uncountable in its general sense, though countable when referring to specific instances or measures.

    Simple

    The doctors are still testing the effectiveness of the new drug.

    In context

    The study aims to evaluate the long-term effectiveness of the government's new environmental policies on urban air quality.

    Pitfall
    The efficiency of the medicine was high. The effectiveness of the medicine was high.

    Efficiency means doing something without wasting time or energy; effectiveness means getting the actual result you wanted.

    ineffectivenessfailurefutility
  2. 02 C1 Advanced FormalTechnical Law

    the state of being in operation or having power.

    the state of being in effect or having the power to produce a required outcome, particularly regarding legal or military force.

    Simple

    The law will reach full effectiveness starting next January.

    In context

    The treaty's effectiveness was compromised by the lack of a clear enforcement mechanism for member states that failed to comply.

    invalidity

Usage effectiveness outweigh · enhance effectiveness · evaluate effectiveness

While she doubts the effectiveness of the Allegra-Pepcid combination, she says it’s “understandable that people turn to things that they can get easily, quickly and less expensively”.

The Guardian· 14 Aug 2026

That air movement improves the effectiveness of your sweating, he says, which is caused by your body naturally trying to cool itself down.

BBC News· 8 Jul 2026

From effective + -ness.

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

This entry
Level C1 · Advanced
Frequency Common
Updated