Families regularly persist in perverted activity? (9)
I believe the answer is:
kinkiness
'perverted activity?' is the definition.
The definition suggests a singular noun which matches the answer.
'families regularly persist' is the wordplay.
'families' becomes 'kin kin' ('kin' means one's family).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'persist' are 'ess'.
'kinkin'+'ess'='KINKINESS'
'in' acts as a link.
Can you help me to learn more?
(Another definition for kinkiness that I've seen is " Peculiarity".)