'untruthful' originates from the prefix 'un-' meaning 'not' and the word 'truthful', which comes from 'truth', meaning 'conformity to fact or reality'.

'untruthful' evolved from the Middle English word 'untrutheful', which combined 'un-' and 'trutheful', eventually becoming the modern English word 'untruthful'.

Initially, it meant 'not in accordance with truth', and this meaning has largely remained the same in modern usage.