posthaste (?.)

• amain
• apace
• at flank speed
• breakneck
• by airmail
• by cable
• by express
• by return mail
• by telegraph
• double-quick
• expeditious
• expeditiously
• express
• fast
• flat-out
• fleet
• full tilt
• hand over fist
• hand over hand
• hastily
• hasty
• hell for leather
• hell-bent
• hell-bent for election
• in double time
• in double-quick time
• in high
• in high gear
• in posthaste
• in seven-league boots
• lickety-cut
• lickety-split
• on the double
• post
• promptly
• quick
• quickly
• rapid
• rapidly
• snappily
• speedily
• speedy
• swift
• swiftly
• trippingly
• under forced draft
• whip and spur
• with all haste
• with giant strides
• with rapid strides
• with speed