Antigender

Antigender is a category of "Genders that can only be defined as the opposite of an existing gender. For instance: antiboy would be the opposite of a boy. antigirl would be the opposite of a girl." The word was coined by asexualjavert and kgmps2. Similarly, ungender (coined by Baaphomett) is a category of genders that are "Not without but a negative; an unboy would be the negative of a boy and an ungirl would be the negative of a girl." (Note that this has a homonym that is widely used in the transgender community: "to ungender" is a verb similar in meaning to the verb "to misgender," that is, to portray someone's gender in a degrading way that they would not have wanted.) Antigenders are under the umbrellas of nonbinary and transgender identities, as well as possibly xenogender.

Specific kinds of antigenders
There are several kinds of antigenders.

antiagender. "similar to aporagender, but defined as the opposite of no gender."

antiaporagender "also similar to aporagender, a gender that is neither masculine nor feminine and has a gendered feeling, but the feeling isn’t specific or strong".

antiboy. The opposite of a boy, but not a girl.

antibigender "a bigender experience where one or both genders are antigenders".

antifluid. "a genderfluid experience where one or more of the genders experienced are antigenders".

antigirl. The opposite of a girl, but not a boy.

cendgender. Coined by anonymous. "From ascend/descend. when your gender changes between one gender and its antigender. the word gender can be replaced be the gender involved, for example cendgirl is when you flip between girl and antigirl". A kind of genderfluid identity.

contragender. Coined by tenderagender. "Someone who deeply defies and identifies opposite or against everything or most things that they associate with their assigned gender. (ex. contragender nb person, contragender trans woman, contragender trans man, etc.)".