"Ain" is a slang word that is commonly used in different English-speaking countries to refer to money. It is often used in informal conversations and might not be understood by everyone. However, there are several other synonyms that one can use instead of "ain" to convey the same meaning. These synonyms include bucks, dough, cash, currency, change, moolah, loot, and greenbacks. These words are widely accepted and can be used in more formal settings. It is important to note that understanding the appropriate context to use these slang words in is crucial as they may not be suitable for professional or formal communication.