Firm hides soldier in shed (5)
I believe the answer is:
rigid
'firm hides' is the definition.
'rigid' can be an answer for 'firm' (I've seen this in another clue). I am not sure about the 'hides' bit.
'soldier in shed' is the wordplay.
'soldier' becomes 'GI' (GI can mean a US soldier).
'in' is an insertion indicator.
'shed' becomes 'rid' (I've seen this in another clue).
'gi' inserted inside 'rid' is 'RIGID'.
Can you help me to learn more?
(Other definitions for rigid that I've seen before include "strict" , "Frozen" , "Stiff and inflexible" , "Incapable of or resistant to bending" , "Uncompromising" .)