The quality of being underneath. / A space (literal or figurative) that is underneath.

The lower surface or part of something. / A background radio sound track played during a specific announcement or program.

Under, below, beneath. / Under the control or power of.

Below; in a place beneath. / On the underside or lower face.

Under, lower.

plural of underneath / (colloquial, childish) genitalia

Synonym of under one's breath

(idiomatic) Alternative form of get under someone's skin