funny
A five (5) letter word that starts with Z and ends with F, there is none recorded. However, there is a word that starts with Z and ends with F. The word is a four (4) letter word: zarf, (noun) a metal holder for a coffee cup.
fiber
A five letter word, second letter F is after or often.
Famished is a word for extremely hungry that starts with the letter F.
farce, fence, force, flare, froze, fudge
"Pressure" is an 8-letter word related to force that starts with the letter "f."
I could only find one word ending in "kr" and it doesn't start with an "f" or have five letters. Perhaps you're thinking of a six-letter word.askr
Forest
Feathers
Frump, flump
falloff
freer