Lavish kisses somewhat revolting, they believe (5)
I believe the answer is:
sikhs
'they believe' is the definition.
(believers in Sikhism)
'lavish kisses somewhat revolting' is the wordplay.
'somewhat' says the answer is hidden in the clue.
'revolting' shows that the letters should be reversed in order.
'shkis' can be found hidden inside 'lavish kisses'.
'shkis' reversed gives 'SIKHS'.
(Other definitions for sikhs that I've seen before include "Believers in religion founded in Punjab" , "Adherents of a Punjab religion" , "Followers of Guru Nanak" , "Followers of an Indian religion" , "certain believers" .)