Foreign agents worked with Resistance (7)
I believe the answer is:
strange
'foreign' is the definition.
(I know that foreign can be written as strange)
'agents worked with resistance' is the wordplay.
'worked with' indicates an anagram.
'resistance' becomes 'r' (electronics abbreviation).
'agents' anagrammed with 'r' gives 'STRANGE'.
(Other definitions for strange that I've seen before include "Unknown or peculiar" , "Odd kind of garnets" , "Bizarre" , "- - Fruit (song)" , "Queer" .)