'undiluted' originates from the prefix 'un-' meaning 'not' and the word 'diluted' from Latin 'dilutus', past participle of 'diluere', meaning 'to wash away'.

'dilutus' transformed into the French word 'diluer', and eventually became the modern English word 'dilute', with 'undiluted' forming by adding the prefix 'un-'.

Initially, it meant 'not washed away or weakened', and this meaning has largely remained the same in modern usage.