Center letter: u
Outer letter: d g n o r t
Answers (40):
  groundout
  donut
  dour
  drug
  dugong
  dugout
  dung
  dunno
  gourd
  gout
  ground
  grout
  grunt
  guru
  noun
  orotund
  outdo
  outdoor
  outgo
  outgun
  outro
  outrun
  rotgut
  rotund
  round
  rout
  rung
  runout
  runt
  tour
  tout
  trout
  turn
  turnout
  tutor
  tutu
  udon
  undo
  unground
  unto