The term 'milk-heavy' is a compound word formed from 'milk' and 'heavy', where 'milk' refers to the dairy liquid and 'heavy' implies a large quantity or density.

The word 'milk' comes from Old English 'milc', while 'heavy' originates from Old English 'hefig'. The combination of these words into 'milk-heavy' is a modern English formation.

Initially, 'milk-heavy' simply described something with a lot of milk, and this meaning has remained consistent.