already - all ready, always - all ways, anyway - any way, somebody - some body .
They are written as one word or two words depending upon the meaning.
I do agree with you it should have been written a while but I think in case of while - awhile the difference is not always clear as with other sound pairs; so the two can be easily confused. The other sound pairs sometimes create problems for native speakers as well:
awhile means for a short time as you said.
For a while means an indefinite period of time (But with the preposition for in BE it means for a short time like awhile)
Perhaps we have to consider BE and AmE differences. In addition for a while (although it means an indefinite period of time) is more common in BE and might even replace awhile particularly in view of the role of English as a global language. There are indications that the two merge and awhile become outdated. (these are only my own observations based additionally on the fact that while is more flexible and can be used in different semantic situations such as contrasting ideas) Furthermore, you can use adjectives such as short, long, little in front of while:
I am going to leave you for a short while.
This is what OED has got to say:
advb. phr. awhyle, 6 a-wyle. [Strictly two words, OE. áne hwíle (for) a while, a space of time: usually written in comb. since 13th c.] (For) a short time, (for) a little.
a1000 Beowulf 3528 Nú is þínes mæ¼nes bl\d áne hwíle. a1250 Owl & Night. 199 Þe ule one hwile hi biþohte. a1300 Cursor M. 10135 Leue Šoure wantounship awhile. 1538 Starkey England ii. iii. 203 Aftur they haue byn brought up in lernyng A-wyle. 1725 De Foe Voy. round World (1840) 104 Sailing awhile to the Southward. 1810 Scott Lady of L. i. xx, Awhile she paused, no answer came.
Improperly written together, when there is no unification of sense, and while is purely a n.
1489 Caxton Faytes of A. i. xxiii. 72 It was doon but awhyle agoon. 1872 Yeats Growth Comm. 102 For awhile the facilities+enabled the Venetians, etc. 1882 Ouida Bimbi 44 After awhile they seemed to pacify each other.