a Of people: steadfast, with unwavering feeling. (Now only in set phrases like "fast friend".) (defdate|from 10th c.)
a Of dyes or colours: not running or fade|fading when subjected to detrimental conditions such as wetness or intense light; permanent (defdate|from 17th c.)
n (British|rail transport) A train that calls at only some stations it passes between its origin and destination, typically just the principal stations
v (intransitive) to abstain from or eat very little food; to abstain from food for religious or medical reasons