'sneakily' originates from the English word 'sneaky', which is derived from the verb 'sneak', meaning 'to move quietly and secretly'.

'sneak' changed from the Old English word 'snican', which meant 'to creep or crawl', and eventually became the modern English word 'sneak'.

Initially, it meant 'to creep or crawl', but over time it evolved into its current meaning of 'to move quietly and secretly'.