Endless opportunity to keep horse and coach (9)
I believe the answer is:
charabanc
'coach' is the definition.
(type of coach or bus)
'endless opportunity to keep horse' is the wordplay.
'endless' means to remove the last letter.
'opportunity' becomes 'chance' (synonyms).
'to keep' indicates putting letters inside.
'horse' becomes 'arab' (Arab is a type of horse).
'chance' with its last letter taken off is 'chanc'.
'chanc' placed around 'arab' is 'CHARABANC'.
'and' is the link.
(Other definitions for charabanc that I've seen before include "Former coach" , "An ABC arch (anag) - early excursion bus" , "Old vehicle" , "Old tourist coach" , "E.g. transport" .)