a long while
Short Period of Time
half a mo'
a short while
I think "while" is not necessarily short-term. "I haven't seen you in quite a while"; "It's been a while since I saw him"; "I haven't seen him for a while" all mean a medium-term period. It specifically means for longer than a short period of time.
As a noun "a while" is simply a period of time. If someone says "I'll see you in a while", you'd want to know whether they meant a short while or a long while. So, I'd suggest "a short while" or "a little while".