undefined

undefined — adjective

1. describing something that is stated or known only in a way that is unclear, impr

1.adjectiveB2
Definition

describing something that is stated or known only in a way that is unclear, imprecise, or open to different interpretations — for example, a role with no fixed duties, or a boundary that has not been drawn exactly.

Example

The exact boundaries of the park remain undefined in the city's planning documents.

remain undefined + location phrase

When Élise joined the team, her main responsibilities were still undefined by the manager.

passive: be + undefined by [person]

Common collocations
  • remain undefined
  • leave something undefined
  • undefined boundaries
  • undefined role
  • undefined term
  • as yet undefined
Synonyms
  • vague

    focuses on lack of precision rather than absence of boundaries; less formal

  • ambiguous

    means open to multiple interpretations, not just unclear

  • unclear

    more general and neutral; the simplest synonym

Antonyms
  • defined

    the direct opposite; clearly stated or described

  • clear

    obvious and easy to understand

  • specific

    exact and detailed

Usage Note

Common in formal and written English. Frequently used with verbs like 'remain,' 'leave,' or 'stay.'

Common Mistakes

The rules are indefinite about overtime.
The rules are undefined about overtime.
'indefinite' means a period with no end; 'undefined' means not clearly stated.

2. lacking a formal statement of its meaning or value; without an explicit definiti

2.adjectiveB2
Definition

lacking a formal statement of its meaning or value; without an explicit definition in a system where one is normally expected — for example, a term in a technical paper with no glossary entry, or a variable in computer code that has not been assigned a value.

Example

The compiler reported an error because the variable 'count' was left undefined in the code.

technical: left undefined in [code/system]

Terms like 'cognitive load' and 'working memory' were left undefined in Dr. Okafor's paper, confusing many readers.

Common collocations
  • left undefined
  • undefined variable
  • undefined term
  • undefined value
  • undefined behavior
Synonyms
  • unspecified

    means not named or mentioned, not necessarily lacking a definition

  • unstated

    means not expressed in words; softer than 'undefined'

Antonyms

Usage Note

Particularly common in computing, mathematics, and lexicography, where formal definitions are expected. In programming, 'undefined' often causes errors at compile time or runtime.

Common Mistakes

❌ 'The law left the crime undefined, so no one was charged.' (The sentence is structurally fine, but 'undefined' in legal contexts more commonly means 'not legally defined' — which is correct here.) This is actually correct usage.

Word family

Synonym discussion

Sense: adjective/1

'Undefined' suggests that something has no clear boundaries, limits, or explanation — it simply has not been made precise. 'Vague' is more subjective: something is vague when the details are missing or kept fuzzy, often because of poor communication ('vague instructions'). 'Ambiguous' means the wording can be interpreted in two or more different ways, which is a distinct problem from being undefined ('an ambiguous sentence'). In everyday use, call something 'unclear' for the simplest option; reserve 'undefined' for formal, technical, or academic contexts where clear definition is expected.

vague ↗ambiguous ↗undefined ↗

Common collocations

Nouns

Adverbs

Phrases

  • left undefined
  • remain undefined
  • stay undefined
  • as yet undefined

Prepositions

Etymology

LatinFrenchEnglish

Formed in English by adding the prefix 'un-' (meaning 'not') to 'defined,' the past participle of 'define.' 'Define' comes from the Latin 'definīre,' which combines 'dē-' (down, away) with 'fīnis' (boundary, limit) — literally meaning 'to set bounds to.' The word has been used since the early 1600s.