A lot vs. Alot: 9 Grammatical Pitfalls
also a.w.o.l., military initialism for absent without leave. The -o- seems to be there mostly so the initialism can be pronounced as a word. In U.S. military use at least from World War II, popular use by 1960.
Absent without leavenoun
A person who is absent without leave (Armed forces fr WWI)