Synonyms for In a flash:

• adj.

  •instantaneous (adjective)
  • most hair trigger,
  • hair trigger,
  • most hair-trigger,
  • more hair-trigger,
  • more hairtrigger,
  • most hairtrigger,
  • more hair trigger.

• adv

  •fast (adverb)
  • in haste,
  • like wildfire,
  • in short order,
  • like greased lightning,
  • like a flash,
  • full tilt,
  • fleetly,
  • like a shot,
  • chop-chop.

• adv.

  •all (adverb)
  • in a flash,
  • outright.
  •fast (adverb)
  • hastily,
  • post-haste,
  • expeditiously,
  • hurriedly,
  • soonest,
  • in nothing flat.
  •hell-for-leather (adverb)
  • like streak,
  • like blue streak,
  • like house on fire,
  • like a house fire.
  •immediately (adverb)
  • in jiffy,
  • in new york minute,
  • un-hesitatingly,
  • doubletime,
  • un hesitatingly,
  • on dot,
  • now never,
  • on spot.
  •instantly (adverb)
  • on dime,
  • there then.
  •on the double (adverb)
  • licketysplit,
  • on double,
  • chop chop.
  •quickly (adverb)
  • like bat out hell,
  • like bat out of hell,
  • like a bat out hell.

• Other synonyms:

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