Expletives (5)
I believe the answer is:
oaths
'expletives' is the definition.
('oath' can be a synonym of 'expletive')
This is the entire clue.
(Other definitions for oaths that I've seen before include "Profane expressions" , "Imprecations" , "professions of loyalty" , "Expletives" , "truths may be established by them" .)