I list armies fighting, concealing current resemblances (12)
I believe the answer is:
similarities
'resemblances' is the definition.
(I've seen this before)
'i list armies fighting concealing current' is the wordplay.
'fighting' indicates an anagram (I've seen this in other clues).
'concealing' indicates putting letters inside.
'current' becomes 'i' (symbol for electric current).
'i'+'list'+'armies'='ilistarmies'
'ilistarmies' anagrammed gives 'simlarities'.
'simlarities' going around 'i' is 'SIMILARITIES'.
(Other definitions for similarities that I've seen before include "things in agreement" , "Parallels" , "Resemblances" .)