Cornice
Etymology
From Italian "cornice" (ledge, frame). Its deeper origin is disputed — proposed sources include Latin "cornix" (crow, perhaps for a beak-like projection) and Greek "korōnis" (a curved line or finishing stroke). The finishing-stroke sense fits its role as the crowning element.
noun · /KOR-nis/
A horizontal molded projection that crowns the top of a wall, building, or column order.
What it names
The decorative "brow" running along the top of a building or a room's ceiling edge — once you can name it you start noticing how it caps and finishes a facade.
Example
Snow gathered on the cornice, tracing a bright line along the top of the old bank.
Related idea
A cornice crowns the very top of a wall or facade; a frieze is the decorated horizontal band that runs just below it. Reading top to bottom, the cornice caps the frieze.