posthaste
Quickly, as fast as someone travelling postQuickly, as fast as someone travelling post; with great speed.
UK/ˌpəʊstˈheɪst/US/ˌpoʊstˈheɪst/
Meaning
1 senses(dated, formal, not comparable)Quickly, as fast as someone travelling post; with great speed.
It is imperative that you finish your task posthaste.
Origin
From the former instruction on letters ‘haste, post, haste’, later reinterpreted as a compFrom the former instruction on letters ‘haste, post, haste’, later reinterpreted as a compound of post + haste.
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