An old thread that I just found while looking for the German for "transom". But I think there are several errors here, making it worthwhile to offer a comment.
First though, a couple of definitions, taken from Merriam-Webster: https://www.merriam-webster.com/dictionary/transom
(a) Transom: "a horizontal crossbar in a window, over a door, or between a door and a window or fanlight above it"
(b) Transom window: "a window above a door or other window built on and commonly hinged to a transom."
The cited article has an illustration, where the "T" points to the transom, and the hinged window above it is a typical transom window.
A fanlight (vd #1) is a special kind of transom window, semi-circular or shaped like a lunette, and is therefore not fully synonymous with transom window. https://www.google.com/search?client=firefox-...,
Finally, Oberlicht (based on the postings cited in #2) in its most frequent meaning seems to be a basement window, and not a transom window at all.
I leave it to others to find a better German translation for transom window. (See the illustration in Merriam-Webster.)
