Fish for old invader (5)
I believe the answer is:
angle
This clue is a double definition.
'fish for' is the first definition.
(thesaurus)
'old invader' is the second definition.
(I've seen this before)
(Other definitions for angle that I've seen before include "A way of approaching" , "member of tribe" , "old invader" , "possibly obtuse" , "Try to catch" .)