When trying to find alternative words for "unheard of," there are plenty of great synonyms to choose from. Some of the most useful options include phrases like "unknown" or "unfamiliar," which get at the sense of something being new or strange to someone. Other possibilities might include "innovative," "original," or "unique," all of which capture the idea of something being different or unusual compared to what came before it. Similarly, words like "unprecedented" or "extraordinary" carry similar connotations, suggesting that something is truly exceptional or one-of-a-kind. Overall, there are plenty of great synonyms for "unheard of" that can help to better capture the sense of something being novel or surprising.