adjective Of the hand, forearm or foot: turned facing away from the body; with the thumb inward or big toe downward.
The hand is in the prone position typically when using a keyboard; and the forearm is then also in the prone position; when the foot is resting on the inner side of the sole, it is in the prone position.
adjective Having a downward inclination or slope.
adjective Shooting from a position while lying down.
adjective Predisposed, liable, inclined, given (to something) (most often, specifically to being befallen by an unsought bad outcome, rather than to undertaking a willful behavior or to having a happy accident).
prone to failure
verb To place in a prone position, to place face down.