WordWeb Online

1. A rate (usually rapid) at which something happens
   "the project advanced with gratifying fastness";
   - speed, swiftness
    
2. The quality of being fixed in place as by some firm attachment
   - fixedness, fixity, fixture, secureness
    
3. A strongly fortified defensive structure
   - stronghold

See also: fast, slow

Type of: defence [Brit, Cdn], defense [US], defensive structure, immovability, immovableness, pace, rate