A half or partially black, half or partially native american person.
"I was dating this guy, he was a nigdian, ugh, sexy-- and he cheated on me with some bitch! So i'm telling him he got me pregnant to make him feel bad."
A black native-american; someone with a black parent and a native-american parent; someone of both african and native descent.
"I was datin' this guy, he's a nigdian; half black, half indian."