arbitrary
gb/ˈɑɹbɪtɹˌɛɹi/ us/ˈɑɹbɪtɹˌɛɹi/
B2
English
~ 6600
Senses
0 senses
adjective
C1
property
1
based on personal will, not reason
Decided in a way that does not follow clear rules or good reason, and may seem like a random or personal choice.
Usage pattern:
an arbitrary [decision/choice/rule/limit]
Common mistake:
Learners often use 'arbitrary' when they only mean 'any' (e.g. *"Choose an arbitrary book"* when they simply mean *"Choose any book"*). 'Arbitrary' usually carries a negative feeling that the choice has no good reason or is unfair, not just that it is free. Learners also sometimes confuse it with 'strict', which has the opposite idea of following firm rules.
Synonyms
random (Suggests lack of clear plan or pattern; can sound less formal and more about chance than about unfairness.)
|
capricious (Stronger sense of sudden change in mood or desire; often more emotional and negative than 'arbitrary'.)
Antonyms
systematic (Stresses following a clear system or method, the opposite of being done without structure.)
|
rational (Highlights being based on good reason and logic, not personal whim.)
Collocations
arbitrary decision
|arbitrary choice
|arbitrary rule
|arbitrary limit
|seem arbitrary
|completely arbitrary
Themes
thinking
|law
|business
|core_vocabulary
Examples
- The manager’s choice of who gets promoted felt completely arbitrary.
- The teacher set an arbitrary deadline that gave us only one day to finish the project.
- The colors on the chart aren’t meaningful; they’re just arbitrary labels.
- Customers complained that the bank’s fees seemed arbitrary and unfair.
Learner examples
- The rules in that game are very arbitrary.
- His decision to move to another city was almost arbitrary.
- The company made an arbitrary change to its return policy.
- The order of the names on the list is arbitrary.
- Many students think the school dress code is arbitrary.
adjective
formal
C1
property
2
using power without legal limits
Used about power or control when someone acts as they want, without following law or being fair.
Usage pattern:
arbitrary [arrest/detention/use of power/rule]
Common mistake:
Learners sometimes use this sense in everyday personal situations where the political or legal meaning is too strong (e.g. *"My mom is very arbitrary"* can sound like she rules like a dictator). For family or workplace contexts, the more general sense of 'unfair' or 'random' is usually better unless you really mean abuse of formal power.
Synonyms
authoritarian (Emphasizes strict control by authority; may follow rules, while 'arbitrary' stresses acting without fair rules.)
|
despotic (Stronger and more emotional; suggests cruel and absolute power, while 'arbitrary' focuses on lack of legal or rational limits.)
Antonyms
lawful (Highlights that actions follow the law, unlike arbitrary actions which ignore or break legal standards.)
|
accountable (Stresses that those in power must explain and justify their actions, unlike arbitrary rule.)
Collocations
arbitrary arrest
|arbitrary detention
|arbitrary rule
|arbitrary power
|arbitrary government
|arbitrary use of authority
Themes
law
|politics
|human-rights
Examples
- Human rights groups condemned the government for arbitrary arrests of protesters.
- Citizens lived in fear of the leader’s arbitrary use of power.
- The court ruled that the travel ban was an arbitrary and unlawful restriction on movement.
- They argued that arbitrary detention without trial violates international law.
Learner examples
- People were angry about the government’s arbitrary arrests.
- In some countries, leaders have almost arbitrary power.
- Arbitrary detention is a serious human rights problem.
- The judge said the new law gave the police arbitrary authority.
- They want to stop arbitrary use of force by the police.
adjective
technical
B2
property
3
any value, not a special one
Used in math, logic, or computing to mean that a number or thing is not special, and can be any value that fits the rule.
Usage pattern:
an arbitrary [number/value/point/function]
Common mistake:
Learners often misunderstand 'arbitrary' in math texts as meaning 'random' in the sense of 'generated by chance'. In many cases it just means 'any value you like', without implying that a random process was used.
Synonyms
any (In technical writing, 'any' is often used in the same way, but 'arbitrary' sounds more formal and precise.)
|
non-specific (Stresses that no particular item is meant, similar to 'arbitrary' in technical contexts but less standard in math writing.)
Antonyms
specific (Means a clearly chosen or identified value, the opposite of an arbitrary one.)
|
fixed (Stresses that the value does not change and has been exactly set.)
Collocations
arbitrary number
|arbitrary value
|arbitrary point
|arbitrary function
|arbitrary constant
Themes
science
|technology
|mathematics
|education
Examples
- Let x be an arbitrary real number greater than zero.
- The algorithm selects an arbitrary element from the list as a starting point.
- We can choose an arbitrary point on the line to illustrate the theorem.
- This function returns an arbitrary value between 0 and 1 for testing purposes.
Learner examples
- Let n be an arbitrary integer.
- Choose an arbitrary point on the circle.
- The program picks an arbitrary number to begin the search.
- We use an arbitrary value here, because the exact value is not important.
adjective
technical
C2
property
4
based on a chosen relative scale
Used about measurements when the numbers are only for comparing things with each other, not for showing a true physical size or amount.
Usage pattern:
an arbitrary [unit/scale/origin/reference point]
Common mistake:
Learners may think 'arbitrary units' means the data are meaningless or incorrect. In fact, it usually means the scale is useful for comparison but not directly tied to a standard physical unit like meters or seconds.
Synonyms
relative (Focuses on values only having meaning in comparison, which is often what 'arbitrary' implies in scientific scales.)
Antonyms
absolute (Describes measurements based on a fixed physical standard, the opposite of arbitrary units or scales.)
|
standardized (Indicates use of agreed, official units, unlike arbitrary ones chosen just for local convenience.)
Collocations
arbitrary units
|arbitrary scale
|arbitrary origin
|arbitrary reference point
Themes
science
|measurement
|technology
Examples
- The fluorescence intensity is reported in arbitrary units on the y‑axis.
- We defined an arbitrary zero point on the scale to simplify the calculations.
- Because the measurements are in arbitrary units, only relative changes are meaningful.
- The diagram shows energy on an arbitrary vertical scale for comparison.
Learner examples
- The graph shows the signal in arbitrary units.
- We use an arbitrary scale to compare the two results.
- This number is in arbitrary units, not in volts or amps.
- Only the shape of the curve matters; the vertical axis is arbitrary.
Grammar
Dictionary form
arbitrary
IPA
GB/ˈɑɹbɪtɹˌɛɹi/
US/ˈɑɹbɪtɹˌɛɹi/
Syllables & stress
ar - bit - rary (3 syllables)
Stress on 1st syllable (ar)
Word forms
Adjective
- Base: arbitrary
Word family
Core family
arbitrarily
adverb
arbitrariness
noun
Related words
Negative and opposite forms
non-arbitrary
adjective
Advanced or less common
arbiter
noun
Expressions
arbitrary and capricious
1/ˈɑɹbɪtɹˌɛɹi ˈænd kəpɹˈɪʃəs/
fixed phrase
formal
unreasonable and unpredictably changing (law)
Used especially in law to describe actions by a government or official that do not follow law or reason and change with personal wishes.
Examples
- The court found the agency’s decision to be arbitrary and capricious.
- Residents argued that the new zoning rules were arbitrary and capricious and should be overturned.
- The judge said the policy changes appeared arbitrary and capricious, lacking any clear justification.
arbitrary arrest
1/ˈɑɹbɪtɹˌɛɹi ɚˈɛst/
fixed phrase
formal
arrest without legal reason
Arresting someone without a clear legal reason or without following the law and fair rules.
Examples
- Witnesses reported arbitrary arrests of peaceful demonstrators.
- The organization monitors cases of arbitrary arrest around the world.
- They filed a complaint over the arbitrary arrest of union leaders.
arbitrary detention
1/ˈɑɹbɪtɹˌɛɹi dɪtˈɛnʃən/
fixed phrase
formal
detention without legal reason
Keeping someone in prison or in custody without a clear legal reason or fair process.
Examples
- International observers condemned the arbitrary detention of journalists.
- The report documents cases of arbitrary detention and torture by security forces.
- Activists are campaigning to end arbitrary detention in the region.