'lice' originates from Old English, specifically the word 'lȳs' (plural of 'lūs'), which came from Proto-Germanic '*lusą'.

'lice' changed from the Old English plural 'lȳs' (singular 'lūs') into Middle English forms such as 'lȝs'/'lyse' and eventually became the Modern English plural 'lice'.

Initially it meant the same thing — the small parasitic insect — and this core meaning has largely remained unchanged into modern usage.