Swears and raves about (5)
I believe the answer is:
avers
'swears' is the definition.
('aver' can be a synonym of 'swear')
'raves about' is the wordplay.
'about' indicates an anagram.
'raves' with letters rearranged gives 'AVERS'.
'and' acts as a link.
(Other definitions for avers that I've seen before include "States positively" , "Declares to be true" , "States firmly - really raves" , "Alleges, asserts" , "States to be true" .)