一旦 [ㄧ ㄉㄢˋ; yi1 dan4]
  in case (sth happens)
  if
  once (sth happens, then...)
  when
  in a short time
  in one day
  ◄ ►
  一旦
  いったん
  adverb (fukushi)
  word usually written using kana alone
  once
  for a moment
  temporarily
  noun (common) (futsuumeishi)
  archaism
  one morning
  ◄ ►