'outside' originates from Old English, specifically the elements 'ūt' + 'sīde', where 'ūt' meant 'out' and 'sīde' meant 'side'.

'outside' changed from Old English 'ūt-sīde' into Middle English forms such as 'ut-side'/'outside' and eventually became the modern English word 'outside'.

Initially it meant 'out, on the outer side', and over time it has largely retained that core meaning while extending to senses like 'the outdoors' and figurative uses.