'plate' originates from Old French, specifically the word 'plate' (feminine), ultimately from Late Latin/Vulgar Latin 'plattus' and from Greek 'platys', where 'plat-'/'platys' meant 'broad, flat'.

'plate' changed from Old French 'plate' (from Late Latin/Vulgar Latin 'plattus' influenced by Greek 'platys') and eventually became the modern English word 'plate'.

Initially it meant 'broad, flat' or 'a flat object'; over time it came to mean specifically 'a flat piece of metal' and then the verb sense 'to cover with a metal layer'.