Eccentric family okay occasionally (5)
I believe the answer is:
kinky
'eccentric' is the definition.
(I've seen this before)
'family okay occasionally' is the wordplay.
'family' becomes 'kin' (synonyms).
'occasionally' indicates alternate letters.
The alternate letters of 'okay' are 'ky'.
'kin'+'ky'='KINKY'
(Other definitions for kinky that I've seen before include "Given to deviant sexual practices" , "Twisted" , "Deviant, eccentric" , "Sexually unusual" , "Irritatingly self-satisfied" .)