'per-year' originates from two elements: 'per' from Latin 'per' (meaning 'through' or 'for each') and 'year' from Old English 'ġēar' (from Proto-Germanic '*jēran').

'per' entered English from Latin usage and has been used in English phrases to mean 'for each'; 'year' evolved from Old English 'ġēar' and related Germanic forms. The compound 'per year' developed in modern English to express a rate measured by year; hyphenated forms like 'per-year' are used attributively.

Initially the parts meant 'through/for each' ('per') and 'a year' ('year'); combined, they came to mean 'for each year' or 'each year', which is the modern usage of 'per-year'.