Custom of riding? (5)
I believe the answer is:
habit
This clue could be a double definition.
'custom' is the first definition.
(habit is a kind of custom)
'riding?' is the second definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'of' acts as a link.
Can you help me to learn more?
(Other definitions for habit that I've seen before include "Custom; clothing" , "It's worn in order" , "Monk's gown or custom" , "Usual practice; garment" , "What might one have a regular tendency to" .)