'improperly-mixed' originates from the combination of 'improperly' and 'mixed'. 'Improperly' comes from the Latin 'improprius', meaning 'not proper', and 'mixed' comes from the Latin 'miscere', meaning 'to mix'.

'Improperly-mixed' evolved from the combination of the words 'improperly' and 'mixed', which have been used in English since the Middle Ages.

Initially, it meant 'not properly combined', and this meaning has largely remained the same in modern usage.