Of course its eighteen holes (5,2,4)
I believe the answer is:
round of golf
'of' is the definition.
Both the answer and definition are singular nouns.
Maybe there's an association between them I don't understand?
'course its eighteen holes' is the wordplay.
I cannot quite understand how this works, but
'course' could be 'golf' (golf course is a kind of course) and 'golf' is present in the answer.
'eighteen holes' could be 'round' (a round of golf includes eighteen holes) and 'round' is found in the answer.
The remaining letters 'of' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?