A bookie and a course (5)
I believe the answer is:
layer
I believe this clue is a double definition.
'a bookie' is the first definition.
(I've seen this in another clue)
'a course' is the second definition.
(I've seen this before)
'and' acts as a link.
(Other definitions for layer that I've seen before include "Stratum; eg, hen" , "Stratum; chicken" , "course" , "Thin sheet - productive hen" , "(Separate) level" .)