Vows of loyalty he's regularly disregarded (5)
I believe the answer is:
oaths
'vows' is the definition.
('oath' can be a synonym of 'vow')
'loyalty he's regularly disregarded' is the wordplay.
'regularly disregarded' means one should take alternating letters (letters removed at regular intervals).
'loyalty'+'hes'='loyaltyhes'
The alternating letters of 'loyaltyhes' are 'OATHS'.
'of' acts as a link.
(Other definitions for oaths that I've seen before include "professions of loyalty" , "Profane expressions" , "truths may be established by them" , "Curses - words of honour?" , "Solemn promises or curses" .)