Pursue a certain line (5)
I believe the answer is:
track
This clue could be a double definition.
'pursue' is the first definition.
(I know that track is a type of pursue)
'a certain line' is the second definition.
'track' can be an answer for 'line' (track is a kind of line). I'm unsure of the 'a certain' bit.
Can you help me to learn more?
(Other definitions for track that I've seen before include "path to follow" , "Follow < course" , "Racing circuit" , "Pathway" , "A prepared course for racing on" .)