The term 'prone to sulking' can be described by four words, all of which have five or four letters. The first word is 'MOPEY', which means to be in a state of low spirits or depression. The second word is 'POUTY', which means to be in a bad mood and express it through facial expressions. The third word is 'MOODY', which means to be easily irritated or prone to sudden changes in mood. The fourth word is 'mopy', which means to be listless and lacking energy. All of these words describe someone who is prone to sulking, meaning they are often in a bad mood and express it through their behavior.