Myxinoidei is a term used to describe a group of jawless fish commonly known as hagfish. The word myxinoidei is derived from the Greek word "myxinos," which means slime or mucus, due to the hagfish's ability to produce large amounts of slime as a defense mechanism. However, there are several synonyms for this term, including Agnatha, which refers to a taxonomic class of jawless fish, Cyclostomata, which encompasses both hagfish and lampreys, and Hyperotreti, which is a subclass within the Agnatha class. While these synonyms may be less commonly used, they provide alternatives to the term myxinoidei that can be used in academic or scientific discussions.