Single female recruited by foreign army branch (6)
I believe the answer is:
ramify
'branch' is the definition.
('ramify' can be a synonym of 'branch')
'single female recruited by foreign army' is the wordplay.
'single' becomes 'i' (one).
'female' becomes 'f' (abbreviation).
'recruited by' is an insertion indicator.
'foreign' is an anagram indicator (foreign order of the letters).
'i'+'f'='if'
'army' with letters rearranged gives 'ramy'.
'if' going inside 'ramy' is 'RAMIFY'.
(Other definitions for ramify that I've seen before include "Divide into branches" , "Split into branches" , "Branch - spread out" , "Produce branches" .)