'gleefully' originates from the Old English word 'glēo', which meant 'entertainment' or 'mirth'.

'glēo' transformed into the Middle English word 'glee', and eventually became the modern English word 'gleeful', with 'gleefully' as its adverbial form.

Initially, it meant 'entertainment or mirth', but over time it evolved into its current meaning of 'showing great joy or delight'.