light a fire under
Also, build a fire under. Urge or goad to action, as in If we don't light a fire under that committee, they'll never do any work. This hyperbolic colloquialism uses light in the sense of “ignite,” a usage dating from the mid-1100s.
Words nearby light a fire under
ligature,
ligeance,
liger,
ligeti,
light,
light a fire under,
light adaptation,
light air,
light armored vehicle,
light artillery,
light as a feather