'ashiver' is formed in English by the addition of the prefix 'a-' (originally a locative/intensive prefix) to the verb 'shiver' (from Middle English 'shiveren'), producing a word meaning 'in a state of shivering.'

'ashiver' appeared in Middle/Early Modern English as forms such as 'ashiveren' or 'ashivern' and later stabilized as 'ashiver' in modern usage; it derives from 'a-' + Middle English 'shiveren' (to shake or quake).

Initially it simply described being 'in a state of shaking' (often physically); the core meaning has remained close to that original sense, though the form is now rare/archaic in contemporary English.