Looking glass and Lens

Looking glass noun - A smooth or polished surface that forms images by reflection.

Lens and looking glass are semantically related in pane or mirror topic. In some cases you can use "Lens" instead a noun phrase "Looking glass".

Lens noun - A transparent optical device used to converge or diverge transmitted light and to form images.

Looking glass and lens are semantically related in thing topic. You can use "Looking glass" instead a noun "Lens", if it concerns topics such as pane or mirror.