means A sum of money given by a government or institution to support a business, industry, or activity deemed worth keeping cheap, viable, or alive.

from From Latin 'subsidium,' which began as a military term meaning a reserve force held in support — the troops waiting in the rear, ready to back up the front line. The root 'sub-' (under, behind) plus 'sedere' (to sit) gives the literal image of those who 'sit behind,' a body held in reserve. It passed into English through Anglo-French in the medieval period, where it shifted from soldiers-in-waiting to money-in-waiting: aid voted by Parliament to support the crown. The sense of 'reserves standing by to prop something up' never really left.