fast

(dated) Firmly or securely fixed in place; stable.

Firm against attack; fortified by nature or art; impregnable; strong.

(of people) Steadfast, with unwavering feeling. (Now mostly in set phrases like fast friend(s).)

Moving with great speed, or capable of doing so; swift, rapid.

(nuclear physics, of a neutron) 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).

Of a place, characterised by business, hustle and bustle, etc.

Causing unusual rapidity of play or action.

(computing, of a piece of hardware) Able to transfer data in a short period of time.

Deep or sound (of sleep); fast asleep (of people).

(of dyes or colours) Not running or fading when subjected to detrimental conditions such as wetness or intense light; permanent.

(obsolete) Tenacious; retentive.

(dated) Having an extravagant lifestyle or immoral habits.

Ahead of the correct time or schedule.

(of photographic film) More sensitive to light than average.