Center letter: r
Outer letter: d g n o t u
Answers (41):
  groundout
  dogtrot
  donor
  door
  dour
  drug
  gorgon
  gourd
  grog
  grotto
  ground
  grout
  grunt
  guru
  odor
  orotund
  outdoor
  outro
  outrun
  rondo
  rood
  root
  rotgut
  rotor
  rotund
  round
  rout
  rung
  runout
  runt
  torn
  toro
  tort
  tour
  trod
  trot
  trout
  turn
  turnout
  tutor
  unground