Course is fixed, containing opposite directions (5)
I believe the answer is:
sweet
'course' is the definition.
(I know that sweet is a type of course)
'fixed containing opposite directions' is the wordplay.
'fixed' becomes 'set' (both can mean decided or determined).
'containing' means one lot of letters goes inside another.
'opposite directions' becomes 'WE' (opposite compass points).
'set' placed around 'we' is 'SWEET'.
'is' is the link.
(Other definitions for sweet that I've seen before include "darling" , "Humbug!" , "Amiable" , "(see 15 across) A Chinese sauce" , "Ewes cycle it (anag) -- herb (myrrh)" .)