Center letter: u
Outer letter: g i n o p r
Answers (37):
  grouping
  pouring
  gouging
  group
  gunning
  guru
  inuring
  inurn
  inurning
  nonunion
  noun
  oppugn
  oppugning
  pinup
  popgun
  pour
  pronoun
  pruning
  punning
  purging
  purr
  purring
  rouging
  ruin
  ruing
  ruining
  rung
  running
  ungroup
  union
  unpin
  unpinning
  unrig
  unrigging
  upon
  upping
  urging