'mirthful' originates from Middle English, specifically the word 'myrthful', where 'myrth' meant 'joy' and '-ful' meant 'full of'.

'myrthful' changed from the Middle English word 'myrthful' and eventually became the modern English word 'mirthful'.

Initially, it meant 'full of joy or happiness', and this meaning has largely remained the same in modern usage.