Shocking extremes of lewdness in Big Brother ? (7)
I believe the answer is:
sibling
'brother ?' is the definition.
(thesaurus)
'shocking extremes of lewdness in big' is the wordplay.
'shocking' is an anagram indicator (I've seen this in other clues).
'extremes of' means to remove the middle letters.
'lewdness' with its centre removed is 'ls'.
'ls'+'in'+'big'='lsinbig'
'lsinbig' anagrammed gives 'SIBLING'.
(Other definitions for sibling that I've seen before include "Bro or sis" , "Maybe brother" , "Brother or sister by the same parents" , "Close relative" , "Bro, perhaps" .)