dispatch: [16] Dispatch appears to have been borrowed from Spanish despachar ‘expedite’, but its ultimate origins are not clear. The likeliest source of the Spanish word is Old French despeechier ‘set free’ (source of modern French dépêcher ‘hurry’), a compound verb formed from the prefix des- ‘un-’ and the verbal element -peechier ‘impede, hinder’, which is also represented in English impeach and goes back ultimately to Latin pedica ‘shackle’.
The semantic history of dispatch thus appears to be ‘unshackle’, ‘set free’, ‘send away, get rid of’, and hence (with the notion of ‘freeing from restraint’) ‘send away quickly’. (The currency of the alternative spelling despatch is due to its occurrence in Dr Johnson’s Dictionary 1755.) => impeach
