1590s, from a noun (1530s) meaning "great speed," usually said to be from "post haste" instruction formerly written on letters (attested from 1530s), from post (adv.) + haste (n.). The verb post "to ride or travel with great speed" is recorded from 1550s.
权威例句
1. Medical aid must be sent to the stricken area posthaste.
灾区需用医药,急如星火.
2. Please come and help me posthaste, I really need you.
请尽快来帮我, 我非常需要你.
3. Please send your answer to me posthaste.
请尽快回信答复我.
4. Note: Anyone who received a signing bonus will be required to return it, posthaste, with interest.