'whithersoever' originates from Old English elements, specifically 'hwider' (whither) + the postpositive element 'soever' (from Old English/Old French), where 'hwider' meant 'to what place' and 'soever' meant 'in whatever manner/extent'.

'whithersoever' changed from Old English components 'hwider' + 'soever' into Middle English forms such as 'whithersoever' or 'whither-soever', and eventually remained in modern English as the archaic/poetic compound 'whithersoever'.

Initially it meant 'to what place' or 'to whatever place', and over time it has retained that core sense but fallen out of regular use, surviving chiefly in literary or archaic contexts meaning 'wherever'.