'insincere' originates from Latin, specifically the word 'insincerus,' where 'in-' meant 'not' and 'sincerus' meant 'clean, pure.'

'insincerus' transformed into the French word 'insincere,' and eventually became the modern English word 'insincere' through Middle English.

Initially, it meant 'not pure or clean,' but over time it evolved into its current meaning of 'not genuine or truthful.'