The answer is fail.
Because there are multiple uses of the word that rhymes with luck and begins with an f.
Firetruck. Or Flying duck. Or Fragile puck. Or flaky muck. The list goes on, really.
firetruck
Fog is a weather related word. It begins with the letter f.
FLU
justunfuf
fake
friendly
Forsooth
fiendishfrenziedfrighteningfrenetic
Some presentations are funny. It begins with the letter f.
flying