Center letter: n
Outer letter: i l o p r u
Answers (29):
  purloin
  inurn
  iron
  lion
  loin
  loon
  noir
  nonillion
  nonunion
  noon
  nori
  noun
  null
  onion
  opinion
  pillion
  pinion
  pinup
  pippin
  poplin
  porn
  porno
  prion
  pronoun
  ruin
  union
  unpin
  unroll
  upon