fastness

IPA/ˈfɑːstnəs/
KK[fˈæstnəs]IPA/ˈfæstnəs/

fastness — noun

  • fastnesssingular
  • fastnessesplural

1. the degree to which something is fixed tightly enough to stay secure instead of

1.nounC2
Definition

the degree to which something is fixed tightly enough to stay secure instead of working loose

Example

Daichi tested the fastness of the bolts before opening the bridge to traffic.

fastness of [something] for secure fixing

Eve worried about the fastness of the baby's car seat on the long drive.

Common collocations
  • test the fastness of
  • check the fastness of
  • fastness of the bolts
  • fastness of a rope
Synonyms
  • firmness

    broader everyday word for something that feels solid or does not give way easily

  • fixedness

    closest formal equivalent; stresses staying in one set position

  • security

    broader and often about safety rather than physical attachment

Antonyms

Grammar Patterns

fastness of [something]

Usage Note

Usually appears in formal descriptions of how firmly an object is fixed in place. Use it for attachment or secure fixing, not for general emotional or political stability.

Common Mistakes

The ladder's fastness kept it from shaking.
The ladder's stability kept it from shaking.
'fastness' is about firm attachment or fixing, not general steadiness or balance.

2. a refuge in a place that enemies cannot easily reach or attack

2.nounC2
Definition

a refuge in a place that enemies cannot easily reach or attack

Example

During the civil war, villagers fled to a mountain fastness above the valley.

pattern: mountain / island / forest fastness

The rebels stored food and medicine in a forest fastness beyond the main road.

Common collocations
  • mountain fastness
  • forest fastness
  • island fastness
  • retreat to a fastness
Synonyms
  • stronghold

    very close in meaning; often used for defended places controlled by a group

  • refuge

    broader and less military; focuses on safety rather than defence

  • hideout

    more informal and stresses secrecy rather than strength

Grammar Patterns

a fastness in/on [place]

retreat to a fastness

Usage Note

Usually literary or historical. It often refers to a mountain, island, forest, or fortress-like refuge that enemies cannot reach easily.

Common Mistakes

The hotel was a fastness near the beach.
The hotel was a refuge near the beach.
'fastness' suggests a place that is hard to reach or defendable, not just any safe place.

3. the quality of moving or happening very quickly

3.nounC2
Definition

the quality of moving or happening very quickly

Example

The hawk's fastness let it seize the rabbit before it reached the hedge.

fastness of an animal's movement

Jabari admired the fastness of the young runner over the final hundred metres.

Common collocations
  • fastness of the river
  • fastness of a runner
  • the fastness with which
  • admire the fastness of
Synonyms
  • swiftness

    closest modern word for quick movement

  • rapidity

    formal word for quick movement or quick development

  • speed

    everyday choice; often also covers measured rate

Antonyms

Grammar Patterns

fastness of [movement/process]

with [adjective] fastness

Usage Note

This sense is rare and old-fashioned. Modern English normally uses 'speed', 'swiftness', or 'rapidity' instead.

Common Mistakes

The car reached a fastness of 120 kilometres per hour.
The car reached a speed of 120 kilometres per hour.
this sense means swiftness in general, not a measured rate in modern usage.

Word family

Synonym discussion

Sense: noun/1

‘Firmness’, ‘fixedness’, ‘stability’, and ‘solidity’ all suggest that something does not give way easily, but they focus on different qualities. ‘Firmness’ is the broad everyday choice for something that feels hard or steady under pressure. ‘Fixedness’ is formal and emphasizes not moving from a set position, so it comes closest to ‘fastness’ in technical writing about bolts, ropes, or fittings. ‘Stability’ is wider: it can describe politics, emotions, prices, or a chair that does not wobble, so it is often too broad when you mean physical attachment. ‘Solidity’ points to strong material or build quality rather than the act of being securely fastened. You might test the fastness of a rope knot, admire the solidity of a stone wall, and rely on the stability of a ladder.

firmness ↗fixedness ↗stability ↗solidity ↗

Etymology

Old EnglishEnglish

Fastness comes from Old English ‘fæstnes’, built on ‘fast’ in its older sense of ‘firm, fixed, or secure’, not its modern sense of ‘quick’. That older meaning still survives in words such as ‘fasten’ and ‘steadfast’. From the idea of being firmly fixed, English developed the noun for firmness and for a safe place that was hard to enter. Later, after ‘fast’ also came to mean ‘quick’, fastness was occasionally used for swiftness too, though that sense is now rare.

First known use

12th century

12th century, in the meaning defined at sense 1