famti gismu

x1 is an aunt/uncle of x2 by bond/tie x3; x1 is an associated member of x2's parent's generation.

Aunt (=fetfamti), uncle (=nakfamti). See also bruna, mamta, mensi, patfu, rirni, tamne.

In notes:

bruna
x1 is brother of/fraternal to x2 by bond/tie/standard/parent(s) x3; [not necess. biological].
mamta
x1 is a mother of x2; x1 bears/mothers/acts maternally toward x2; [not necessarily biological].
mensi
x1 is a sister of/sororal to x2 by bond/tie/standard/parent(s) x3; [not necessarily biological].
patfu
x1 is a father of x2; x1 begets/sires/acts paternal towards x2; [not necessarily biological].
rirni
x1 is a parent of/raises/rears x2; x1 mentors/acts parental toward child/protege x2.
tamne
x1 is cousin to x2 by bond/tie x3; [non-immediate family member, default same generation].
fetfamti
fa1=fe1 is an aunt of fa2 by bond/tie fa3.
nakfamti
n1=f1 is an uncle of f2 by bond/tie f3.
selfamti
x1 is an niece/nephew of x2 by bond/tie x3.
pentu
x1 is a non-binary sibling of/to x2 by bond/tie/standard/parent(s) x3; [not necessarily biological].
tcuti
x1 is a sibling of a direct ancestor/elder of x2 by bond/tie/relation/standard x3 (not necessarily genetic/biological nor necessarily directly ancestral); x1 is an associated member of one of x2's ancestor's generation; x1 is an (great-(great-(...)))uncle/aunt of x2.
abvele
x1 is a grandparent of x2 by bond/tie/relation/standard x3 (not necessarily genetic/biological nor necessarily directly ancestral); x1 is an associated member of x2's parent(s)'s parent(s)'s generation.