'irresponsibly' originates from the Latin word 'irresponsabilis', where 'ir-' meant 'not' and 'responsabilis' meant 'answerable'.

'irresponsabilis' transformed into the French word 'irresponsable', and eventually became the modern English word 'irresponsible', with 'irresponsibly' as its adverbial form.

Initially, it meant 'not answerable', but over time it evolved into its current meaning of 'lacking responsibility'.