What does fastness mean?
Fastness is a noun describing the state of being firmly fixed, secure, or difficult to dislodge. It has two main uses in modern English. The first refers to a strongly fortified or naturally inaccessible place — a castle, citadel, or mountain retreat — that serves as a safe refuge against attack; writers often speak of partisans or rebels holding out in a remote mountain fastness. The second use denotes durability or permanence, especially the resistance of dyes and colours to fading or running, a meaning still standard in the textile industry under terms like colour fastness. Both senses descend from the older meaning of the adjective 'fast', which signified firm and immovable long before it came to mean quick. Though never common, fastness carries a literary, slightly old-fashioned air, evoking strength, safety, and endurance. It remains useful wherever precision about security or permanence matters, and its unusual history — a word of firmness born from an adjective now synonymous with speed — makes it especially memorable.
nounThe quality of being firmly fixed, secure, or resistant to change; also a strongly fortified or secure place of refuge.
- A strongly fortified or inaccessible place serving as a secure refuge.
- The quality of being firmly fixed or secure; resistance to being moved, loosened, or worn away (as in the fastness of a dye or colour).
- Rarely, speed or rapidity, reflecting the later 'fast = quick' sense of the root word.
"The rebels withdrew to a mountain fastness beyond the reach of the army."
"Partisans held out for months in their mountain fastness."
"Buyers were assured of the colour fastness of the newly dyed fabric."
The plural is regular and typically appears when referring to multiple strongholds or refuges.
"The rebels retreated to their scattered mountain fastnesses."
The same word 'fast' that today means speedy originally meant 'firmly fixed' — which is why a 'fastness' is a stronghold you can't break into, not a fast runner.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of fastness
Fastness was formed in English from the adjective 'fast' plus the suffix '-ness', with 'fast' deriving from Old English 'fæst', meaning firm, fixed, or secure. That ancient sense of immovability persists in expressions like 'holding fast' and 'steadfast'. Only centuries later did 'fast' develop its familiar meaning of rapid, likely influenced by the idea of running firmly or vigorously. Cognates include the German 'fest' and related forms in other Germanic languages.
How fastness is actually used
Fastness is a somewhat formal or literary word. The 'fortified refuge' sense appears mostly in historical or descriptive writing, while the 'firmness/permanence' sense survives most naturally in technical contexts such as textile manufacture (colour fastness). The speed-related sense is rare and largely historical.
Easily confused with fastness
Fatness means the condition of being fat or obese, while fastness means firmness, security, or a fortified refuge — the two merely look similar in spelling.