Synonyms for In an instant:

• adv.

  •early (adverb)
  • freshly,
  • timely,
  • right away,
  • instantly,
  • betimes,
  • soon,
  • promptly,
  • directly,
  • straightaway,
  • first,
  • recently,
  • instantaneously,
  • summarily,
  • presto,
  • primitively,
  • newly,
  • without delay,
  • thereon,
  • thereupon,
  • in no time,
  • seasonably,
  • in a jiffy,
  • soonest,
  • at once.
  •tout de suite (adverb)
  • pronto,
  • now.

• n.

  •in a flash (noun)
  • flash.

• Other synonyms:

  •Other relevant words:
  • in a flash,
  • in a trice,
  • in a twink,
  • in a moment,
  • in a jiff,
  • Fust,
  • in a second,
  • in a twinkling.

Antonyms for In an instant:

• adv.

  • early
    later, late.