'disregardful' originates from the prefix 'dis-' meaning 'not' or 'opposite of' and the word 'regard,' which comes from Old French 'regarder,' meaning 'to look at' or 'to consider.'

'regarder' transformed into the Middle English word 'regarden,' and eventually became the modern English word 'regard.' The prefix 'dis-' was added to form 'disregardful.'

Initially, it meant 'not considering or looking at,' and this meaning has largely remained the same in modern usage.