'directionally' originates from Latin via Middle English and the adjective formation, specifically from Latin 'directio' (from the verb 'dirigere') where the elements 'di-/dir-' conveyed 'to' or 'apart' and 'regere' (root) meant 'to guide/straighten'.

'directionally' changed from Middle English 'direction' (from Latin 'directio') to the adjective 'directional' by adding the suffix '-al', and then the adverbial suffix '-ly' produced the modern English 'directionally'.

Initially related to the act or process of directing or pointing (the noun 'direction'); over time it evolved into an adjectival and then adverbial form meaning 'relating to direction' or 'in terms of direction' (and figuratively 'in terms of general trend').