annual expenditure
General term for yearly spending; less common than the Diet-member sense.
We need to cut the company's annual expenditure.
annual salary for Diet members
Specifically the yearly allowance paid to members of the Japanese Diet; a fixed political term.
The annual salary for Diet members is stipulated by law.
Compound of 歳 (さい, 'year') and 費 (ひ, 'expense'). The specific sense of Diet members' salary developed from the idea of annual public expenditure allocated for their compensation.