foment
To incite or cause troublesome acts; to encourage; to instigate.
transitive
He was arrested for fomenting a riot; after all, it's bad enough being in a riot but starting one is much worse.
To apply a poultice to; to bathe with a cloth or sponge.
transitive
Sties in the eye are irritating and disfiguring. Foment with warm water; at night apply a bread-and-milk poultice.
Where it comes from
From Middle English fomenten, a borrowing from Old French fomenter, from Late Latin fōmentāre, from Latin fōmentum (“lotion”), from fovēre (“heat, cherish”).
Adapted from the Wiktionary entry foment (CC BY-SA 4.0).