light a fire under
(redirected from build a fire under)light a fire under (someone or something)
To motivate someone or something to take action. The deadline really lit a fire under us—we never would have gotten all that work done otherwise. Something must have lit a fire under Jenna—she has really started taking her schoolwork seriously.
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.
light a fire under
To urge or move to action.