Center letter: a
Outer letter: d e h n o p
Answers (51):
  headphone
  openhanded
  added
  addend
  addenda
  aeon
  ahead
  anode
  anon
  aped
  apnea
  append
  appended
  daphne
  dapped
  dead
  deaden
  deadened
  deadhead
  deadheaded
  deadpan
  deadpanned
  dean
  doodad
  ennead
  hand
  handed
  happen
  happened
  head
  headed
  heap
  heaped
  henna
  hennaed
  naan
  nada
  nana
  nape
  napped
  neap
  padded
  paean
  panda
  pane
  paned
  panned
  papa
  peahen
  peapod
  poppa