4 letter words:
burg7,
grub7,
grum7,
brut6,
turm6,
guru5,
trug5,
3 letter words:
bum7,
bug6,
gub6,
gum6,
mug6,
bru5,
bur5,
but5,
mut5,
rub5,
rum5,
tub5,
tum5,
umu5,
urb5,
gur4,
gut4,
rug4,
tug4,
rut3,
utu3,
2 letter words:
mu4,
um4,
gu3,
ug3,
ur2,
ut2,