Xynthari is a singular gender identity, just like female, male, juxera, etc. It is a gender that is derived but distinctly separate from androgyny and xeninity. Xynthari is a single gender that is derived from both androgyny and xeninity, but is a single gender, not a mix of the two, and is still completely unrelated to how xenine people and androgyne people experience their (respective) xeninity and androgyny.
Xynthari is not a combination of androgyne and xenine (xendrogyne), nor does it describe someone who is multigender who is both liaspec and xiaspec or has xenogenders. It is a distinctly separate gender from the two: derived from them but experienced as a singular, completely coalesced gender that relates heavily to qualities of androgyny described in an entirely xenine way. That experience is core to the gender but is still separate from "standard" androgyny and xeninity.
It's important to note that xynthari is a gender, not a gender identity, alignment, modality, etc. Someone who is xynthari would say "I am xynthari" or "I am xyntharian", not "I am a xynthari". Someone can be aligned with being xynthari, but it is not in and of itself an alignment, as it's a complete gender, not just an alignment or quality. Since xynthari is derived yet fully separate and distinct from androgyny and xeninity, xynthari people may or may not identify as outherine and/or xiaspec.
The masculine version of xynthari is xynthvir, the feminine version of xynthari is xynthera, and the outherine version of xynthera is xynthouri.
River Symbol
The symbol for xynthari people is a river because, in nature and in many cultures, rivers are portrayed as being derived from both feminine and masculine aspects and qualities, but they are still entirely separate from femininity and masculinity in a way that connects the gender experience to non-standard xeninity, making rivers the perfect symbol for xynthari people.
History
The term xynthari was coined by FANDOM user Reign of the queerios on a blog post on March 11, 2021, along with its masculine, feminine, and outherine equivalents.