'loathsome' originates from Old English, specifically the word 'lāðsum,' where 'lāð' meant 'hateful' and '-sum' was a suffix forming adjectives.

'lāðsum' transformed into the Middle English word 'lothsum,' and eventually became the modern English word 'loathsome'.

Initially, it meant 'hateful or causing loathing,' and this meaning has largely remained the same in modern usage.