Rai stones are a type of currency used by the indigenous people of Yap Island, Micronesia. Interestingly, there are several synonyms for the term "rai stones". One commonly used synonym is "fei", which refers to a type of stone that is similar to the rai stones but slightly smaller in size. Another synonym for rai stones is "yapese stone money", as the stones are native to Yap Island. The term "megalithic money" is also used to describe the rai stones due to their immense size and weight, which can range up to four tons. Regardless of the term used, rai stones are still a fascinating and unique form of currency that have been used for centuries by the people of Yap Island.