headroom

n.

净空，头上空间，（拱梁等下面的）净空高度；

1. There's a lot of headroom for such a small car.
   这么小的一辆汽车的头上空间蛮大的。
2. There is not enough headroom for buses to go under this bridge.
   这座桥梁下面的净空高度不够，公共汽车不能通行。

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