Synonyms for In a flash:

• adv

  •fast (adverb)
  • like a shot,
  • like greased lightning,
  • in haste.

• adv.

  •all (adverb)
  • instantaneously,
  • outright.
  •fast (adverb)
  • hastily,
  • hurriedly,
  • expeditiously.

• Other synonyms:

  •
  • apace,
  • pronto.
  •
  • quickly,
  • Posthaste.
  •Other relevant words:
  • hell-for-leather,
  • swiftly,
  • quick,
  • in a wink,
  • in a trice,
  • like lightning,
  • unexpectedly,
  • in a second,
  • briskly,
  • double-quick,
  • in an instant,
  • in no time,
  • promptly,
  • precipitately,
  • flat out,
  • abruptly,
  • rapidly,
  • in a moment,
  • suddenly,
  • right away.