Fentanyl, or fent, used to refer to a street opiate stronger than heroin. Thought to be a mistaken pronunciation of “fent” as in “fet-a-nyl”. Also called fetty for the same reason.
“Hey man, gimme some of those dirty 30’s”
“Yeah, the ones with fet?
A blunt or spliff filled with heroine, Crack, and sometimes weed.
Yo Joe want to come smoke a fet.
A shorthand for feter (fet rhymes with get), which is a unit of length measurement defined as a quarter of a meter. It's close to the unit of feet and is thus pronounced as "feeter", which rhymes with and is spelled in the same manner as meter. It's a compromise unit between imperial and metric systems.
Look at that giant dude! He must be at least eight fets tall!