Definition for Post-haste:

• To perform an act as rapidly as possible.

Synonyms for Post-haste:

• adj.

  •fast (adjective)
  • in a jiffy,
  • Lickety Split,
  • presto,
  • chop-chop.

• adv.

  •fast (adverb)
  • expeditiously,
  • in haste,
  • like a flash,
  • apace,
  • like greased lightning,
  • hurriedly,
  • like a shot.
  •hastily (adverb)
  • fast,
  • suddenly,
  • precipitately.

• Other synonyms:

  •Other relevant words:
  • flat out,
  • flat,
  • instantly,
  • on the run,
  • instantaneously,
  • without delay,
  • briskly,
  • at once,
  • rapidly,
  • speedily,
  • like lightning,
  • at full tilt,
  • immediately,
  • p.d.q.,
  • directly,
  • in no time,
  • in a trice,
  • right away,
  • at full speed,
  • with dispatch,
  • quickly,
  • once,
  • like the wind,
  • quick,
  • straight away,
  • promptly,
  • straightaway,
  • swiftly,
  • in a wink,
  • pronto,
  • hastily.

Antonyms for Post-haste:

• adj.

  • fast
    plodding, unhurried, tardy.
  • quick
    sluggish, lazy.

• a. & adv.

  • posthaste
    eventually, slowly, slow.

• adv.

  • hastily
    delayed.
  • pell-mell
    cautiously, carefully.
  • promptly
    negligently, late.
  • rapidly
    leisurely.
  • soon
    never, far, later, distant.
  • swiftly/swift
    sluggishly.