expression, godan verb (-gu)
lie in wait; wait for a chance to attack
Idiomatic expression derived from the literal image of a predator sharpening its fangs before striking. Used for someone biding their time, ready to harm or take revenge.
彼は復讐の機会を狙って、密かに牙を研いでいる。
He is secretly lying in wait for a chance to take revenge.
ライバル会社は市場シェアを奪おうと牙を研いでいる。
The rival company is sharpening its fangs, waiting to seize market share.