'average-sized' originates from the combination of 'average' and 'sized', where 'average' meant 'typical or common' and 'sized' referred to 'having a particular size'.

'average' changed from the Old French word 'avaria' and eventually became the modern English word 'average'. 'Sized' comes from the Old French 'sise', meaning 'size'.

Initially, 'average' meant 'a financial term for dividing costs', but over time it evolved into its current meaning of 'typical or common'.