In lang=en terms the difference between fast and fist
is that
fast is firmly or securely fixed in place; stable while
fist is to fist-fuck.
In intransitive terms the difference between fast and fist
is that
fast is to abstain from food, or eat very little, especially for religious or medical reasons while
fist is to break wind.
As an adjective fast
is firmly or securely fixed in place; stable.
As an adverb fast
is in a firm or secure manner, securely; in such a way as not to be moved .
As an interjection fast
is short for "stand fast", a warning not to pass between the arrow and the target.
As an initialism FIST is
future Infantry Soldier Technology.