'self-indulgent' originates from the combination of 'self' and 'indulgent', where 'indulgent' comes from Latin 'indulgere', meaning 'to be kind or lenient'.

'indulgere' transformed into the Old French word 'indulgent', and eventually became the modern English word 'indulgent'.

Initially, it meant 'to be lenient or kind', but over time it evolved into its current meaning of 'characterized by excessive indulgence in one's own desires'.