'greatcoat' originates from the English words 'great' and 'coat', where 'great' meant 'large' or 'heavy' and 'coat' referred to an outer garment.

'greatcoat' has been used in English since the 17th century to describe a large, heavy coat worn over other clothing.

Initially, it meant 'a large coat', and this meaning has largely remained the same in modern usage.