Synonyms of fastness

fastness

noun

ˈfas(t)-nəs 

1

as in speed

a high rate of movement or performance

the amazing fastness with which the boy took his shower had us wondering if he'd used any water

Synonyms & Similar Words

• speed
• velocity
• rate
• hurry
• rapidity
• quickness
• swiftness
• celerity
• speediness
• pace
• rapidness
• fleetness
• haste
• acceleration
• gait
• tempo
• precipitation
• expedition
• promptness
• clip
• alacrity
• promptitude
• expeditiousness
• rush
• hustle
• hastiness
• drive
• dispatch
• precipitousness
• warp speed

Antonyms & Near Antonyms

• slowness
• sluggishness
• lethargy
• reluctance
• torpidity
• languor
• torpor
• deliberation
• languidness
• leisureliness
• deliberateness
• lateness
• procrastination
• dilatoriness
• pokiness

2

as in stronghold

a structure or place from which one can resist attack

the guerillas retreated to their network of hidden fastnesses deep within the mountains

Synonyms & Similar Words

• stronghold
• fortress
• bastion
• citadel
• fortification
• castle
• fort
• rampart
• parapet
• redoubt
• bunker
• hold
• bulwark
• earthwork
• breastwork
• battlement
• embattlement
• blockhouse
• dugout
• alcazar
• casbah
• garrison house

3

as in loyalty

adherence to something to which one is bound by a pledge or duty

his uncompromising fastness to the cause of freedom was beyond question

Synonyms & Similar Words

• loyalty
• allegiance
• dedication
• commitment
• devotion
• fidelity
• steadfastness
• faithfulness
• adhesion
• constancy
• fealty
• attachment
• piety
• faith
• devotedness
• troth
• affection
• reliability
• dependability
• resolution
• determination
• fondness
• firmness
• trustworthiness
• trustability
• trustiness

Antonyms & Near Antonyms

• treachery
• inconstancy
• disloyalty
• perfidy
• falsity
• faithlessness
• infidelity
• unfaithfulness
• falseness
• separation
• alienation
• perfidiousness
• disaffection
• estrangement

Example Sentences

Recent Examples of fastness

The redyed fabrics showed uniform color uptake and washing and rubbing fastness comparable to the reference fabric, according to the study. — Alexandra Harrell, Footwear News, 26 Aug. 2026

Editors and contributors compare dozens of sets and look for qualities such as softness, durability, breathability, color fastness, and how well the linens launder and withstand wear. — Yelena Moroz Alpert, Architectural Digest, 20 Jan. 2026

Li said the color builds the familiar ring-dye, white-core look designers expect, then fades predictably in laundry while maintaining high light fastness (Grade 4–5) and strong anti-yellowing. — Angela Velasquez, Sourcing Journal, 11 Nov. 2025

Like the pressing, the hard work mentality and fastness of transition for example. — Andy Jones, New York Times, 29 May 2025

The Neutral Ground had cowboys (or Cow Boys), Indians, cavalry attacks and rescues, and secret woodland fastnesses known only to the canniest frontiersman. — Ian Frazier, The New Yorker, 15 July 2024