'boastfulness' originates from Middle English, specifically the word 'boasten,' where 'boast' meant 'to speak with excessive pride.'

'boasten' transformed into the modern English word 'boastfulness' through the addition of the suffix '-fulness' to denote the quality of being boastful.

Initially, it meant 'to speak with excessive pride,' and this meaning has largely remained the same in modern usage.