Female Nunh?

[Miyha]

I... would really like to know where you're getting this "third gender" impression from.

For a male Seeker of the Sun, there are only two positions available—breeding males (nunh – pronounced ‘noon’) and all others (tia – pronounced ‘tea-ah’). All males are born as tia. At any time in their lives, a tia can challenge the tribe nunh to battle. If the tia is victorious, he takes the nunh’s place as tribe breeding male (until he is challenged and defeated), and the nunh becomes a tia once again (if he survives the ordeal).

Nunh and Tia are essentially titles bestowed upon male Seekers of the Sun that proclaim their status within the tribe. They are not their own genders by any means... Idek where you got that one. >< There are also no known tribes without males as far as I know and I don't see there being a male-less tribe any time soon... And even if there were?

It is very unlikely that they'll grow a weiner and become able to successfully breed, which is all the Nunh status entails.

Nunh = breeding male. Used for breeding. As in they do the impregnating. So... yeah. See above. ;;;;

EDIT: If you are interested in a female only tribe though and it's not totally lore breaking to create your own small one (Idk how often this would be done in Seeker culture, and afaik it hasn't been done in cannon), it could make sense. The leading female obviously wouldn't be a Nunh, just a tribe leader. I could see a female only tribe working somewhat like the Borlaaq Xaela tribe:

A tribe of all women. While breeding with men from other tribes is allowed, if a male is born into the tribe, he is given up within a year of birth.