A fixed sum of money due annually, e.g. tax, rent or something in kind. Later, the sum paid for the licence to collect monies, e.g. taxes from a city. Moneyers had the farm, in their case for minting coins. It was a gathering in of plenty, which in usage became the agricultural farm as we use the word. [< Lat. firma = a fixed payment; OldEngl. feorm = rent in kind, tribute] -
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.