adjective. Located, placed, or used under the arm.

adjective. Executed with the hand brought forward and up from below the level of the shoulder; underhand.

adverb. With an underarm motion or delivery.

noun. The armpit.

noun. The armpit.

noun. Old-fashioned and now outlawed style of bowling in cricket.

adjective. For use under the arm.

"From the photo (on Grumperina's blog?), the sleeves seem to be very stretchy and slightly set in; the "underarm" stretches enough to cover the shoulder point without being too bulky under the arms."

Arm  alarm  arm  charm  disarm