Initially missing? (4)
I believe the answer is:
awol
'missing?' is the definition.
(I've seen this in another clue)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for awol that I've seen before include "Absent without leave (abbrev.)" , "Of soldier, illegally absent - initially" , "'Absent without permission, initially (4)'" , "Not present when supposed to be" , "Missing without permission" .)