Причастие прошедшего времени
Rare but attested; means to place someone/something (or oneself) in a prone position.
Определения
To position (a person or object) so that it is lying flat, especially face downward. The therapist carefully proned the patient to improve ventilation.
To move or lie oneself in a prone position, often with the particle "out." The marine proned out behind the sandbag wall.