To lie in wait for something; to be on the lookout and ready, often waiting in ambush or expectancy.
警察が出口で犯人を待ち構えていた。
The police were lying in wait for the criminal at the exit.
犬が門のところで来客を待ち構えている。
The dog is waiting at the gate for visitors.
彼は次のチャンスを待ち構えているようだ。
He seems to be waiting for the next opportunity.