'asininely' ultimately originates from Latin, specifically the word 'asinus', where 'asinus' meant 'ass' or 'donkey'.

'asininely' derives from the adjective 'asinine', which entered English in the early 17th century from Neo-Latin 'asininus' (from Latin 'asinus'), and the adverb was formed by adding the suffix '-ly' to 'asinine'.

Initially it referred to 'pertaining to or resembling an ass (donkey)', but over time it evolved into the current sense of 'extremely stupid or foolish', with the adverb meaning 'in a stupid or foolish manner'.