7 letter words:
grubber12,
6 letter words:
rubber10,
burger9,
5 letter words:
gebur8,
regur6,
urger6,
4 letter words:
burb8,
berg7,
burg7,
grub7,
brer6,
burr6,
rube6,
grue5,
urge5,
ruer4,
3 letter words:
bub7,
ebb7,
beg6,
bug6,
gub6,
brr5,
bru5,
bur5,
reb5,
rub5,
urb5,
erg4,
gue4,
gur4,
reg4,
rug4,
err3,
rue3,
ure3,
2 letter words:
be4,
gu3,
ug3,
er2,
re2,
ur2,