'diathermic' originates from Greek, specifically the word 'diathermikos,' where 'dia-' meant 'through' and 'thermos' meant 'heat.'

'diathermikos' transformed into the French word 'diathermique,' and eventually became the modern English word 'diathermic.'

Initially, it meant 'allowing heat to pass through,' and this meaning has largely remained the same in modern usage.