The term 'BELIEVER's Suffix' refers to a set of four words that all end with the same suffix. The first word is 'ISM, ' which is a noun that describes a system of beliefs or principles. The second word is 'ite, ' which is a noun that refers to a follower of a particular belief or cause. The third word is 'ist, ' which is a noun that refers to someone who practices or believes in a particular system of thought. The fourth word is 'ists, ' which is a plural form of the word 'ist.' All four words are related to the concept of belief and can be used to describe someone who follows a particular set of beliefs.