Ambassador beginning to ignore common sense? Disgraceful (7)
I believe the answer is:
heinous
'disgraceful' is the definition.
(thesaurus)
'ambassador beginning to ignore common sense?' is the wordplay.
'ambassador' becomes 'he' (His or Her Excellency).
'beginning to' indicates taking the first letters.
'common sense?' becomes 'nous' (nous is a kind of common sense).
The initial letter of 'ignore' is 'i'.
'he'+'i'+'nous'='HEINOUS'
(Other definitions for heinous that I've seen before include "Hateful" , "Dreadful" , "Despicable" , "Extremely evil" , "Revolting" .)