'ashake' originates from the English prefix 'a-' combined with the verb 'shake', where the prefixed 'a-' conveyed a state ('in' or 'on') and 'shake' comes from Old English 'sceacan' meaning 'to move quickly or to cause to move'.

'ashake' formed in Middle English by prefixing 'a-' to 'shake' (from Old English 'sceacan'); the construction follows a pattern seen in other adjectives/adverbs like 'awake' or 'adrift'.

Initially used to indicate being 'in a state of shaking' or 'shaken'; its basic sense of 'shaken/unsteady' has been largely preserved, though the prefixed form is now rare or archaic in modern usage.