FASTNESS
stronghold, fastness
(noun) a strongly fortified defensive structure
fastness, fixedness, fixity, fixture, secureness
(noun) the quality of being fixed in place as by some firm attachment
speed, swiftness, fastness
(noun) a rate (usually rapid) at which something happens; “the project advanced with gratifying speed”
Source: WordNet® 3.1
Etymology
Noun
fastness (countable and uncountable, plural fastnesses)
A secure or fortified place; a stronghold, a fortress.
The state of being fast.
Firmness, security.
Rapidity, swiftness.
The ability of a dye to withstand fading.
Source: Wiktionary
Fast"ness, n. Etym: [AS. fæstnes, fr. fæst fast. See Fast, a.]
1. The state of being fast and firm; firmness; fixedness; security;
faithfulness.
All . . . places of fastness [are] laid open. Sir J. Davies.
2. A fast place; a stronghold; a fortress or fort; a secure retreat;
a castle; as, the enemy retired to their fastnesses in the mountains.
3. Conciseness of style. [Obs.] Ascham.
4. The state of being fast or swift.
Source: Webster’s Unabridged Dictionary 1913 Edition