farmyoudaoicibaDictYouDict[farm 词源字典]
farm: [13] The specifically agricultural connotations of farm are surprisingly recent. The word comes ultimately from Latin firmāre ‘make firm, fix’, which produced a medieval Latin derived noun firma, denoting ‘fixed payment’. English acquired the word via Old French ferme, and originally used it in just this sense (‘I will each of them all have 4d to drink when they pay their farm’, Bury Wills 1463); something of this early sense is preserved in the verbal usage farm out, which to begin with signified ‘rent out’.

By the 16th century the noun was shifting semantically from ‘fixed (rental) payment’ to ‘land leased for such payment, for the purpose of cultivation’, but only very gradually did the notion of a farm being specifically a leased piece of land die out.
=> firm[farm etymology, farm origin, 英语词源]
farm (n.)youdaoicibaDictYouDict
c. 1300, "fixed payment (usually in exchange for taxes collected, etc.), fixed rent," from Old French ferme "a rent, lease" (13c.), from Medieval Latin firma "fixed payment," from Latin firmare "to fix, settle, confirm, strengthen," from firmus "firm" (see firm (adj.)).

Sense of "tract of leased land" is first recorded early 14c.; that of "cultivated land" (leased or not) is 1520s. A word of confused history, but there is agreement that "the purely agricultural sense is comparatively modern" [Century Dictionary]. There is a set of Old English words that appear to be related in sound and sense; if these, too, are from Latin it would be a very early borrowing. Some books strenuously defend a theory that the Anglo-Saxon words are original (perhaps related to feorh "life").

Phrase buy the farm "die in battle," is at least from World War II, perhaps a cynical reference to the draftee's dream of getting out of the war and going home, in many cases to a peaceful farmstead. But fetch the farm is prisoner slang from at least 1879 for "get sent to the infirmary," with reference to the better diet and lighter duties there.
farm (v.)youdaoicibaDictYouDict
mid-15c., "to rent (land)," from Anglo-French fermer, from ferme "a rent, lease" (see farm (n.)). The agricultural sense is from 1719. Original sense is retained in to farm out.