Look in to restrain son being obnoxious (9)
I believe the answer is:
loathsome
'obnoxious' is the definition.
(thesaurus)
'look in to restrain son' is the wordplay.
'look' becomes 'lo'.
'in' becomes 'athome' ('at home' can be similar in meaning to 'in'**).
'to restrain' means one lot of letters goes inside another.
'son' becomes 's'.
'athome' going around 's' is 'athsome'.
'lo'+'athsome'='LOATHSOME'
'being' acts as a link.
(Other definitions for loathsome that I've seen before include "15 [ABHORRENT]" , "Detestable" , "gross" , "Hateful" , "Disgusting, nauseating" .)