'indoors' originates from the combination of 'in' and 'doors', where 'in' meant 'inside' and 'doors' referred to 'entrances or exits of a building'.

'indoors' changed from the Old English word 'inn' meaning 'inside' and 'duru' meaning 'door', eventually becoming the modern English word 'indoors'.

Initially, it meant 'inside the doors', but over time it evolved into its current meaning of 'inside a building'.