unfasten

unfasten — verb

1. to make something that was closed or fixed become open or loose — like undoing a

1.verbtransitive / intransitiveB1
Definition

to make something that was closed or fixed become open or loose — like undoing a seatbelt or unbuttoning a shirt — or for something that is closed or fixed to become open or loose by itself.

Example

Before getting out of the taxi, Yasmin unfastened her seatbelt and picked up her bag.

transitive: unfasten + [object] (seatbelt)

Linh carefully unfastened the tiny buttons on her baby's jacket before bath time.

Common collocations
  • unfasten your seatbelt
  • unfasten a button
  • unfasten a buckle
  • unfasten a clasp
  • unfasten a latch
  • unfasten a strap
  • come unfastened
Synonyms
  • undo

    broader in scope — 'undo' works for knots, zips, buttons, and even digital actions

  • loosen

    less complete — 'loosen' means to make less tight without necessarily fully opening

  • release

    more formal — 'release' is typical for catches, locks, and safety mechanisms

  • unbuckle

    more specific — only applies to objects closed with a buckle

Antonyms
  • fasten

    direct opposite — to close or attach something securely

  • fasten up

    especially for clothing and bags

Grammar Patterns

unfasten + [object]

[fastening] unfastened

come unfastened

Usage Note

Can be used both transitively (someone unfastens a fastened object) and intransitively (the fastening comes undone by itself or accidentally). The pattern 'come unfastened' is common for describing an accidental or unnoticed loosening.

Common Mistakes

I unfastened the knot in the rope.
I untied the knot in the rope.
'unfasten' sounds unnatural for knots and laces; use 'untie' instead.

Word family

  • fasten
    verbB1
  • fastener
    nounB2
  • fastening
    nounB2
  • unfastened
    adjectiveB2
  • unfastening
    nounC1

Synonym discussion

Sense: verb/1

'Unfasten' is the most general word for opening or releasing a mechanical fastener — seatbelts, buckles, clasps, and buttons. 'Undo' is broader and can apply to knots, laces, and even software commands (undo typing), making it the most versatile. 'Loosen' suggests making something less tight without fully opening it (loosen a belt after a meal). 'Release' has a more formal or mechanical feel and is commonly used for catches, locks, and safety restraints (release the emergency brake). 'Unbuckle' is the most specific and only works for buckles. For example, you unfasten a car seat but unbuckle a sandal; you loosen a tie but release a dog leash.

undo ↗loosenrelease ↗unbuckle

Common collocations

Nouns

Adverbs

Phrases

  • come unfastened
  • work itself unfastened

Prepositions

Etymology

Old EnglishMiddle EnglishEnglish

Formed in Middle English by combining the prefix 'un-' (meaning 'reverse of, undo the action') with the verb 'fasten' (from Old English 'fæstnian', meaning 'to make firm or secure'). The result is 'to reverse the action of fastening' — that is, to undo or release something that was previously closed or attached. The prefix 'un-' is one of English's most productive reversative prefixes, and 'unfasten' follows the same pattern as 'unlock', 'untie', and 'unbutton'.