Center letter: o
Outer letter: g i k n u w
Answers (33):
  unknowing
  ginkgo
  going
  gong
  gonging
  goon
  gouging
  gown
  gowning
  know
  knowing
  known
  kook
  noggin
  nonunion
  nook
  noon
  noun
  oink
  oinking
  ongoing
  onion
  owing
  owning
  union
  unknown
  unwon
  winnow
  winnowing
  wino
  wonk
  wooing
  wowing