to encourage or instigate (trouble, discord, etc); stir up
(med) to apply heat and moisture to (a part of the body) to relieve pain and inflammation
fomentation (ˌfəʊmɛnˈteɪʃən) noun fomenter, noun
Both foment and ferment can be used to talk about stirring up trouble: he was accused of fomenting/fermenting unrest. Only ferment can be used intransitively or as a noun: his anger continued to ferment (not foment); rural areas were unaffected by the ferment in the cities
C15: from Late Latin fōmentāre, from Latin fōmentum a poultice, ultimately from fovēre to foster
c.1400 (implied in fomentation), from M.Fr. fomenter, from L.L. fomentare, from L. fomentum "warm application, poultice," from fovere "to warm, cherish, encourage." Extended sense of "stimulate, instigate" (1620s) was in the French. Related: Fomented; fomenting.