Top beginner of course remains (5)
I believe the answer is:
crest
'top' is the definition.
(crest can mean the top of a hill)
'beginner of course remains' is the wordplay.
'beginner' suggests taking the first letters (I've seen 'Beginners' mean this).
'remains' becomes 'rest' (both can mean what's left over).
The first letter of 'course' is 'c'.
'c'+'rest'='CREST'
(Other definitions for crest that I've seen before include "Top point of hill or wave" , "Top (of wave etc)" , "Tuft" , "Surmount" , "Summit ridge" .)