the trouble with 8 is, it seems no one under the age of 40 knows transom!

or the most common idiom using it.. to come in over the transom--

transom windows are, i think are different than fan lights.. a fan light is a semi circle window above a door.. and it is fixed.

a transom is rectangluar, and opens by turning on a pivot.

the idiom come from the idea of poor (that is, lacking money) writers who would put manuscripts "in over the transom" and so save the postage, and its used to describe anything of dubious value that arrived unsolicited..

transoms where used alot in the days before A/C-- since they were above the door, and usually to small for a person to fit through, they could be left open, and the hot air would rise, and vent through the transom.

when i was a kid, and live in "new law tenements" (circa, 1880) apartments, the apartments all had transoms..