Could be armed force (5)
I believe the answer is:
might
This clue could be a double definition.
'could' is the first definition.
(synonyms)
'armed force' is the second definition.
'might' can be an answer for 'force' (I've seen this before). I'm unsure of the 'armed' bit.
'be' acts as a link.
Can you help me to learn more?
(Other definitions for might that I've seen before include "Capability" , "Great power/strength" , "- - and main" , "Great power, strength" , "word expressing possibility" .)