the.com/architrave

means The horizontal band of molding that runs along the top of columns, resting directly on the capitals — the lowest of the three main parts of a classical entablature.

from From Italian architrave, itself a splice of Greek arkhi- ('chief, principal,' the same prefix in 'architect') and Latin trabs ('beam'). So the word is literally 'chief beam' — a plain structural label dressed up by centuries of classical architecture into a term of art.