big bum
If you mean end rhyme, 'fun' rhymes.
Smart gun
blowgun
The devils gun
caffiened nun
electron gun, favorite son, submachine gun, cinnamon bun
One word that rhymes with pun is "fun."
spun fun shun gun none
Bosher, dosher, osher and sacher
Gun
A word that rhymes with lunchroom is mushroom.
Gun, fun, ton, run, bun, shun