fastest

Adjective

fast (comparative faster, superlative fastest)

1. (dated) Firmly or securely fixed in place; stable.
   • That rope is dangerously loose. Make it fast!

   Synonyms:

   firm, immobile, secure, stable, stuck, tight

   Antonyms:

   loose

2. Firm against attack; fortified by nature or art; impregnable; strong.
   • out-lawes […] lurking in woods and fast places1596 (date written; published 1633), Edmund Spenser, A Vewe of the Present State of Irelande […], Dublin: […] Societie of Stationers, […], →OCLC; republished as A View of the State of Ireland […]...

   Synonyms:

   fortified, impenetrable

   Antonyms:

   penetrable, weak

3. Steadfast, with unwavering feeling. (Now mostly in set phrases like fast friend(s).)
   • I still hear you sayin', "Dear one, hold me fast"1933, Will Hudson, Irving Mills, Eddy DeLange, Moonglow
4. Moving with great speed, or capable of doing so; swift, rapid; light.
   • I am going to buy a fast car.

   Synonyms:

   quick, speedy, light

   1. (nuclear physics) Having a kinetic energy between 1 million and 20 million electron volts; often used to describe the energy state of free neutrons at the moment of their release by a nuclear fission or nuclear fusion reaction (i.e., before the neutrons have been slowed down by anything).
      • Plutonium-240 has a much higher fission cross-section for fast neutrons than for thermal neutrons.
5. Of a place, characterised by business, hustle and bustle, etc.
   • Sydney is a fast city, and the pace is becoming increasingly more frantic.1968, Carl Ruhen, The Key Club, Sydney: Scripts, page 15

See all 28 meanings of fast