The central wedge-shaped stone of an arch that locks its parts together.

拱顶石，塞缝石拱的中部楔形石头，使拱的各个部分连在一起。

youdao

The building is equipped with central air-conditioning system, air system, computer management system, IDD, DDD telephone and IC electronic locks and other scientific and advanced hardware facilities.

楼内配有中央空调系统、新风系统、微机管理系统、IDD、DDD电话以及IC卡电子锁等科学先进的硬件设施。

youdao

Fresh from constructing a sea-level canal through the flat Egyptian sand, de Lesseps was determined, without having set foot in Panama and after only the vaguest of topographical studies, that his project through the mountainous central American isthmus would also be a sea-level canal, requiring no locks to cope with changes in altitude.

ECONOMIST: The Panama Canal