Imagine being armed, perhaps (5)
I believe the answer is:
dream
'imagine' is the definition.
(dreaming is a kind of imagining)
'armed perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'armed' anagrammed gives 'DREAM'.
'being' acts as a link.
(Other definitions for dream that I've seen before include "Part of sleep" , "Vision, fantasy" , "King had one" , "Fantasy; imagine" , "Nocturnal vision" .)