to promote the growth or development of, to rouse or incite.
If you had sore muscles in the 1600s, your doctor might have advised you
to foment the injury, perhaps with heated lotions or warm wax. Does
this sound like an odd prescription? Not if you know that "foment"
traces to the Latin verb "fovēre," which means "to heat." The earliest
documented English uses of "foment" appear in medical texts offering
advice on how to soothe various aches and pains by the application of
moist heat. But the idea of applying heat can also be a metaphor for
stimulating or rousing to action. Within 50 years of its English debut,
"foment" was also being used in political contexts to mean "to stir up,"
"to call to action," or, in a sense at least figuratively opposite to
its original one, "to irritate."