past participle of fall under

to get past an obstruction by going underneath, although with difficulty:

Synonym of under the microscope

(circus) One who is at the base of a formation of acrobats in a performance, as of a human pyramid.

To subdue.

To the leeward.

under one's breath; spoken very softly

(military) Equipped with weapons (of a country, army etc.); in a state of armed, military readiness.

(idiomatic, location) So as to be hidden from plain view (and thus easily ignored or overlooked).

(UK, informal) subjected to (figurative) pressure; under the gun