Heading north over line, I stare (4)
I believe the answer is:
ogle
'stare' is the definition.
(I've seen this before)
'heading north over line i' is the wordplay.
'heading north' shows that the letters should be reversed in order.
'over' means one lot of letters goes inside another.
'line' becomes 'l'.
'i' becomes 'ego' (I've seen this in other clues).
'l' going within 'ego' is 'elgo'.
'elgo' reversed gives 'OGLE'.
(Other definitions for ogle that I've seen before include "Leer" , "Give the glad eye" , "Stare amorously" , "Gawp" , "Look flirtatiously at" .)