English Reference
verb · noun

alter

v. · n.
US /ˈɔɫtɝ/ UK /ˈɒltɐ/ al·ter UK spelling alters

  1. 01 B2 Upper Intermediate Academic

    v.to change something slightly, often to make it better or more suitable.

    v.to make a structural or formal change to something without replacing it entirely.

    Simple

    We had to alter our travel plans because the flight was cancelled.

    In context

    The researchers were forced to alter their hypothesis after the initial data revealed a significant correlation they had not previously considered.

    Usage

    Often used with a direct object; can also be used without an object to mean 'to become different'.

    Pitfall
    He went to the church to pray at the alter. He went to the church to pray at the altar.

    Do not confuse 'alter' (to change) with 'altar' (a table used in religious ceremonies).

  2. 02 B2 Upper Intermediate

    v.to change a piece of clothing so that it fits you better.

    v.to adjust the dimensions of a garment for a better fit.

    Simple

    The trousers were too long, so I took them to a tailor to have them altered.

    In context

    She decided to alter the vintage dress herself, narrowing the waist and shortening the hem to create a more contemporary silhouette.

    tailoradjustresize
  3. 03 C1 Advanced American English Medicine

    v.to perform a medical operation on an animal so it cannot have babies.

    v.to castrate, neuter, or spay a domestic animal.

    Simple

    The animal shelter requires all owners to alter their pets before adoption.

    In context

    Veterinarians generally recommend that owners alter their dogs at a young age to prevent unwanted litters and certain health complications.

    neuterspayfix
  4. 04 C2 Proficiency Technical Psychology

    n.one of several different personalities that a person might have in some mental health conditions.

    n.a distinct personality state or identity within an individual, typically associated with dissociative identity disorder.

    Simple

    The patient described how an alter would sometimes take control during stressful moments.

    In context

    Clinical observation focused on the transition between the primary identity and a protective alter during the therapeutic session.

    Usage

    Used as a countable noun in clinical psychology.

Usage alter balance · alter behaviour · alter course

This can alter natural flow patterns and reduce the amount of water in rivers.

Phys.org· 14 Aug 2026

And readers can alter their votes after reacting to comments.

Ars Technica· 10 Aug 2026

Etymology 1

From Old French alterer (French altérer), from Medieval Latin alterāre (“to make other”), from Latin alter (“the other”), from al- (seen in alius (“other”), alienus (“of another”), etc.; see alias, alien, etc.) + compar. suffix -ter.

Etymology 2

Probably from alter ego.

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

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