for, using, or relating to one eye

The images you see are only half as bright as they would be with a traditional monocular eyepiece. 你看到的图像，和用传统单眼目镜看到的图像相比，亮度只有一半。

Binoculars or clip-on monocular telescopes are conventionally used to observe sporting events or for bird watching. 双眼望远镜或是可夹住的单眼望远镜，用在观看体育活动或观鸟上很方便。

a tube with a glass lens (= a curved piece of glass, plastic, or other transparent material) at either end that you look through to see things that are far away more clearly

He watches television, mostly sports, with a monocular. 他用一个单筒望远镜看电视，主要是看体育节目。

There's also a waterproof nocturnal monocular for watching in the dark. 还有一个防水的夜间单筒望远镜，可以在黑暗中使用。