English Reference
noun

deviation

n.
US /ˌdiviˈeɪʃən/ UK /dˌiːvɪˈeɪʃən/ de·vi·a·tion UK spelling deviations

  1. 01 B2 Upper Intermediate

    a difference from what is usual or expected.

    the act of departing from an established course, principle, or standard.

    Simple

    Any deviation from the original plan must be approved by the manager.

    In context

    The committee noted a significant deviation from the safety protocols during the inspection of the chemical plant.

  2. 02 C1 Advanced Technical Math

    the difference between a particular value and the average value of a group.

    the difference between an observed value and the arithmetic mean of a distribution.

    Simple

    The standard deviation shows how much the test scores vary from the average.

    In context

    A low standard deviation indicates that the data points tend to be very close to the mean of the set.

    Usage

    Often used in the phrase 'standard deviation' to describe how spread out numbers are.

  3. 03 B2 Upper Intermediate Science

    a move away from a planned path or direction, such as a plane changing course to avoid a storm.

    a physical departure from a planned or regular course, especially in navigation or transport.

    Simple

    The pilot requested a deviation to the south to avoid the heavy clouds.

    In context

    The ship's deviation from its charted course was necessary to avoid the approaching hurricane, though it delayed the arrival by two days.

Usage standard deviation

In terms of surprise, however, there were only minor deviations from the reference values.

Phys.org· 17 Aug 2026

This helps to capture any potential “butterfly effect,” says Alet, where a small deviation from a trend could lead to much bigger changes down the line.

Ars Technica· 8 Aug 2026

From Middle French deviation, from Medieval Latin deviatio. Morphologically deviate + -ion.

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

This entry
Origin la-med deviatio
Level B2 · Upper Intermediate
Frequency Frequent
Updated