Unconventional family occasionally okay (5)
I believe the answer is:
kinky
'unconventional' is the definition.
(similar in meaning)
'family occasionally okay' is the wordplay.
'family' becomes 'kin' (synonyms).
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
The alternate letters of 'okay' are 'ky'.
'kin'+'ky'='KINKY'
(Other definitions for kinky that I've seen before include "Deviant, eccentric" , "Given to deviant sexual practices" , "Twisted" , "Irritatingly self-satisfied" , "Given to unusual sexual behaviour" .)