伺机
sì jī · HSK 7
to wait for an opportunity
👁️⏳ 伺 = watch/spy + 机 = opportunity, chance — so: watch for the chance
伺 means to watch or spy on; 机 is opportunity (the same 机 as 机会, opportunity). Together they mean to lie in wait until the right moment comes. The sounds sì jī run close to the English see-key: watch for the key moment.