I. (ˈ) ̷ ̷| ̷ ̷ noun
Etymology: post (IV) (courier) + haste
archaic : speed in traveling (as of a post or courier) : great haste — used chiefly in the phrase in posthaste
II. adverb
: with great speed : in great haste : by the fastest possible means
riding posthaste
sent posthaste for his lawyer
III. adjective
obsolete : speedy , immediate
requires your haste, posthaste appearance — Shakespeare