'assidually' originates from Latin, specifically the adjective 'assiduus', where 'ad-' (or assimilated 'as-') meant 'to/toward' and 'sedere' meant 'to sit'.

'assidually' developed as an adverbial form from Latin 'assiduus' (via Late Latin/Medieval Latin) through English adaptations such as 'assiduous' and the more common adverb 'assiduously', with 'assidually' appearing as a rarer variant.

Initially related to the idea of 'sitting near' or 'being present' (from 'assidere'), it evolved to mean 'persistent, constant, diligently present' and now conveys the sense of diligent or persistent effort.