Stretch out in park on course (7)
I believe the answer is:
recline
'stretch out' is the definition.
(thesaurus)
'park on course' is the wordplay.
'park' becomes 'rec' (I've seen this in other clues).
'on' means one lot of letters go next to another.
'course' becomes 'line' ('line' can be a synonym of 'course'**).
'rec'+'line'='RECLINE'
'in' is the link.
(Other definitions for recline that I've seen before include "Lie back to rest" , "Lie back and take it easy" , "Lean back, relax" , "Lie back and relax" , "Assume horizontal or leaning position as for rest" .)