The term "little green man" is often used to describe an imaginary extraterrestrial being. However, there are several synonyms for this term that can be used in different contexts. Some of these synonyms include "alien," "Martian," "ET," "space creature," "UFO occupant," "extraterrestrial," "little grey man," and "visitor from another planet." These words may be used interchangeably, depending on the specific context in which you are using them. If you are writing science fiction, you may opt for the term "alien," while in a more casual conversation, "little green man" or "ET" could be more appropriate.