Fish in corner (5)
I believe the answer is:
angle
I believe this clue is a double definition.
'fish' is the first definition.
(angle can mean to fish)
'corner' is the second definition.
(eg a corner of a shape)
'in' acts as a link.
(Other definitions for angle that I've seen before include "Right, acute or obtuse" , "Heat (metal) and allow to cool to remove stresses" , "A way of approaching" , "Gradient" , "Point of view; old tribesman" .)