'phthisical' originates from Greek, specifically the word 'phthisikos,' where 'phthisis' meant 'consumption' or 'wasting disease.'

'phthisikos' transformed into the Latin word 'phthisicus,' and eventually became the modern English word 'phthisical.'

Initially, it meant 'related to consumption or wasting disease,' and this meaning has largely remained the same in modern usage.