Reefer is a slang term for cannabis or marijuana. This word has gained popularity among the youth culture and has led to the creation of several synonyms. One such synonym is "weed," which is commonly used for cannabis. Another word used for cannabis is "pot." Apart from these, there are several other slang terms used for cannabis, including "grass," "bud," "herb," and "Mary Jane." These terms are commonly used by cannabis enthusiasts and can vary from region to region. However, it's important to note that while these terms might be commonly known as synonyms for cannabis, they are still illegal in many parts of the world.