Shy, joined the army again? (8)
I believe the answer is:
reserved
I believe this is a double definition.
'shy' is the first definition.
(reserved can mean shy or timid)
'joined the army again?' is the second definition.
(served in the army again)
(Other definitions for reserved that I've seen before include "without emotion" , "Retiring" , "Uncommunicative, not extrovert" , "Slow to show emotion" , "Held back, set aside" .)