English has the words brother and sister, but then we also have the word sibling as a gender-neutral version. We have the words aunt and uncle as well, but no gender-neutral version. What languages have such a word? Are there any that have such a word and don't have gender-specific options at all?
I'll offer that in Khmer there is only a gender-neutral term for older siblings of your parents, អ៊ុំ /ʔom/. The terms for younger siblings of your parents are gender-specific, មីង /miːŋ/ for females and ពូ /puː/ for males.
Like the Thai example cited in the comments, these are honorific terms not restricted to family, however unlike Thai, there is no general distinction between paternal and maternal aunts and uncles. For more information on Khmer honorifics, here is a decent blog post on the subject.