Fast″ness, n. [AS. fæstnes, fr. fæst fast. See Fast, a.] 1. The state of being fast and firm; firmness; fixedness; security; faithfulness.
All... places of fastness 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. Ascham.
4. The state of being fast or swift.