adjective Firmly or securely fixed in place; stable. .mw-parser-output .defdate{font-size:smaller}
That rope is dangerously loose. Make it fast!
adjective Firm against attack; fortified by nature or art; impregnable; strong.
adjective Steadfast, with unwavering feeling. (Now mostly in set phrases like fast friend(s).)
adjective Moving with great speed, or capable of doing so; swift, rapid; light.
I am going to buy a fast car.
adjective 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.
adjective Of a place, characterised by business, hustle and bustle, etc.
adjective Causing unusual rapidity of play or action.
a fast racket, or tennis court
adjective Able to transfer data in a short period of time.