Said when either yes or no is the appropriate answer. It is up to the listener to determine the meaning from context. Example: Gee, that's bad news. Yeahnah, its not that bad. OR Gee, that's bad news. Yeahnah, it really freaks me out.
YEAHNAH
Meaning of YEAHNAH in English
Slang English vocab. Английский сленговый словарь. 2012