An ace in the hole is an argument, plan or thing kept hidden until needed.

VOA: special.2009.11.22

you make a little hole, and go in with an instrument instead of making an incision.

医生会先打开一个小孔，将仪器伸进去。而不是像以前一样做一个切口。

MIT用数字说话 - SpeakingMax英语口语达人

The researchers estimate that the five-hole flute would produce an even wider mix of notes.

VOA: special.2009.08.18

The trench is an extremely deep hole on the floor of the Indian Ocean.

VOA: special.2009.03.17

Visitors can also enjoy an evening at the Jackson Hole Playhouse.

VOA: special.2009.02.16