'holly' originates from Old English, specifically the word 'holegn', which referred to the holly tree.

'holly' changed from Old English 'holegn' into Middle English forms such as 'holin'/'holly' and eventually became the modern English word 'holly'.

Initially it meant the same plant (the holly tree); over time the form and spelling stabilized to the current word 'holly', and it retained its botanical meaning (plus use as a personal name).