The word "cosher" is relatively uncommon, and as such, it is difficult to find an antonym that is also well-known. However, some possible opposites of "cosher" may include "forbidden," "prohibited," "illegal," "non-kosher," "unclean," "taboo," "impermissible," or "off-limits." These words carry negative connotations, implying that something is not allowed or is considered morally or religiously unacceptable. In contrast, "cosher" refers to something that is acceptable or permitted according to Jewish dietary laws. While there is no one perfect antonym for "cosher," these options may offer a sense of the word's opposite meanings.