Far-out is a slang term that is commonly used to describe something that is unusual, extreme, or unconventional. There are many different synonyms that can be used in place of far-out, depending on the context and the tone of the conversation. Some common synonyms include eccentric, outlandish, bizarre, odd, unconventional, unique, and quirky. Other possible synonyms include radical, unusual, offbeat, peculiar, freakish, and nontraditional. Each of these terms has a slightly different connotation, so it's important to choose the right synonym for the specific situation. However, they all convey a sense of something that is unconventional or surprising.