Center letter: u
Outer letter: a d g i n r
Answers (36):
  guardian
  guarding
  arguing
  augur
  auguring
  aura
  drug
  drugging
  druid
  dung
  dunning
  durag
  durian
  during
  gauging
  grudging
  guar
  guard
  guiding
  gunning
  guru
  iguana
  inuring
  inurn
  inurning
  nudging
  ragu
  ruin
  ruing
  ruining
  rung
  running
  undid
  unrig
  unrigging
  urging