'upside' originates from Middle English, specifically the word 'up' combined with 'side', where 'up' meant 'above' and 'side' referred to 'aspect'.

'up' and 'side' were combined in Middle English to form 'upside', eventually becoming the modern English word 'upside'.

Initially, it referred to the 'upper side' of something, but over time it evolved into its current meaning of 'advantageous aspect'.