for awhile/ for a while

[Maybo]

The path between the chainlink fence and the Mile 81 rest area was, by Pete's estimation, about half a mile long, and there were Big Kid signposts all along the way: half a dozen small brown bottles (two with snot-caked coke spoons still attached), empty snack bags, a pair of lace-trimmed panties hanging from a thornbush (it looked to Pete like they'd been there for awhile, like maybe fifty years), and - jackpot! - a half-full bottle of Popov vodka with the screw cap still on. (The Bazaar of Bad Dreams by Stephen King)

What's the difference between "for a while" and "for awhile"?

 

[emsr2d2]

I'm shocked to be saying this when referring to my favourite author, but "for awhile" is wrong because "awhile" means "for a while".

I'm going to rest here awhile.
I'm going to rest here for a while.

 

[5jj]

Some elderly Brits never write it as one word.