1 [predic.] (prone to/prone to do something) likely to or liable to suffer from, do, or experience something, typically something regrettable or unwelcome:years of logging had left the mountains prone to mudslideshe is prone to jump to conclusions
2lying flat, especially face downward:I was lying prone on a foam mattressa prone position
technical denoting the position of the forearm with the palm of the hand facing downward.
3 archaic with a downward slope or direction.
late Middle English: from Latin pronus 'leaning forward', from pro 'forward'