1. The state of being swift; the state of being fast and firm; firm adherence; strength; security; a stronghold; a fortress; a castle.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• fiotness,
• fastiners,
• fittness,
• ftness,
• fastners,
• wistness,
• fastnere,
• fattness,
• fastes,
• fasners,
• firtness,
• fastner,
• fastesn,
• fastenes,
• fotness,
• faseners,
• feintness,
• fasness,
• fastnesse,
• fastnes

• fasten,
• faction,
• fastens,
• fasting,
• fastener,
• fast one,
• fastened.

The adjective form of the word "fastness" is "fast".

The plural of the "fastness" can be the "fastnesses".

The singular of the "fastness" can be the "fastness".