Vehicles used by oddly vain clergymen (6)
I believe the answer is:
vicars
'clergymen' is the definition.
(vicar is a kind of clergyman)
'vehicles used by oddly vain' is the wordplay.
'vehicles' becomes 'cars' (car is a kind of vehicle).
'used by' says to put letters next to each other.
'oddly' means one should take alternating letters.
The alternate letters of 'vain' are 'vi'.
'cars' after 'vi' is 'VICARS'.
(Other definitions for vicars that I've seen before include "Members of clergy in charge of churches" , "Ministers" , "clergymen" , "those taking tarts to party" .)