Center letter: i
Outer letter: a d e n p x
Answers (37):
  appendix
  adenine
  aide
  aided
  apian
  denied
  died
  dine
  dined
  dipped
  eddied
  idea
  inane
  indeed
  index
  indexed
  indie
  innie
  naiad
  nannied
  nine
  ninepin
  nipped
  nixed
  paid
  pain
  pained
  panini
  pied
  pine
  pined
  pinned
  pinniped
  pipe
  piped
  pippin
  pixie