Corner at 90 — that needs precise approach (5,5)
I believe the answer is:
right angle
'corner at 90' is the definition.
(90 degree angle)
'precise approach' is the wordplay.
'precise' becomes 'right' (both can mean accurate).
'approach' becomes 'angle' (as in a journalist's approach to a story).
'right'+'angle'='RIGHT-ANGLE'
'that needs' acts as a link.
(Other definitions for right angle that I've seen before include "That between perpendicular and base" , "Part of a square" , "that's formed by 1 Across and Down" , "Ninety degree corner" , "corner of the square" .)