For use under the arm.

(transitive) To supply with insufficient weaponry.

The underside of an animal. / The underside of any thing. / (figuratively) The side which is not normally seen, normally a dark, immoral place.

The small trees and other plants that clutter the floor of a forest.

(transitive) To clear (an area) of underbrush. / (intransitive) To work among the underbrush.

To achieve less than expected; to fail to fulfil one's potential.

The London underground railway system.

(transitive, intransitive) To dress in insufficiently warm clothes. / (transitive, intransitive) To dress in insufficiently formal clothes.

Done by moving the hand (and arm) from below. / Sly, dishonest, corrupt, cheating. / Insincere; sarcastic. / Secret; surreptitious. / Understaffed.

In an underhanded manner.