'overpromise' originates from the prefix 'over-' meaning 'excessively' and the word 'promise' from Latin 'promittere', where 'pro-' meant 'forward' and 'mittere' meant 'to send'.

'promittere' transformed into the Old French word 'promettre', and eventually became the modern English word 'promise'. The prefix 'over-' was added to form 'overpromise'.

Initially, 'promise' meant 'to send forward a pledge', but 'overpromise' evolved to mean 'to pledge excessively'.