'forty-nine' originates from Old English elements for the two parts: 'feowertig' (forty) and 'nigon' (nine), where 'feower' meant 'four' and 'tīene/teg' (in 'feowertig') meant 'ten', and 'nigon' meant 'nine'.

'forty' came from Old English 'feowertig' and evolved through Middle English 'forti'; 'nine' came from Old English 'nigon' (Middle English 'nine'); the compound 'forty-nine' developed by combining the two words and became the modern English 'forty-nine'.

Initially the elements referred literally to 'four tens' and 'nine'; over time the compound has retained the same numeric meaning and now denotes the single number 'forty-nine'.