Horseman kept customs alive in horseless vehicle (8)
I believe the answer is:
cavalier
'horseman' is the definition.
(I've seen this before)
'customs alive in horseless vehicle' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'alive' is 'valie' which is within the answer.
'vehicle' could be 'car' (car is a kind of vehicle) and 'car' is present in the leftover letters.
No letters remain.
This explanation may well be incorrect...
'kept' is the link.
Can you help me to learn more?
(Other definitions for cavalier that I've seen before include "Arbitrary, off-hand" , "Horseman" , "... King Charles, spaniel" , "supporter of the monarchy" , "High-handed, supercilious" .)