* If you are looking for the opposite gender: The opposite of "frau" would be "mann" (German for "man").
* If you are looking for a word that means "not a woman": This would be "kein Mann" (German for "not a man") or "kein Mensch" (German for "not a person").
* If you are looking for a word that means "opposite of feminine": This would be "männlich" (German for "masculine").
It is important to understand the context in which you want to use the word "opposite" to determine the most appropriate translation.