Second-floor family? (10)
I believe the answer is:
background
'family?' is the definition.
(thesaurus)
'second-floor' is the wordplay.
'second' becomes 'back' (to second a motion is to back it).
'floor' becomes 'ground' (ground floor is a kind of floor).
'back'+'ground'='BACKGROUND'
(Other definitions for background that I've seen before include "kind of music" , "history" , "player's obscure position" , "(A person's) experience, education, circumstances" , "Environment" .)