United island to block ambassador for good (6)
I believe the answer is:
humane
'good' is the definition.
(thesaurus)
'united island to block ambassador' is the wordplay.
'united' becomes 'U' (abbreviation).
'island' becomes 'man' (the Isle of Man is an example).
'to block' means one lot of letters goes inside another (block can mean to fill a hole in something).
'ambassador' becomes 'he' (His or Her Excellency).
'u'+'man'='uman'
'uman' put into 'he' is 'HUMANE'.
'for' acts as a link.
(Other definitions for humane that I've seen before include "Kind and liberal" , "Inflicting minimal pain" , "Showing compassion or consideration for others" , "Merciful and considerate" , "Kind and sympathetic" .)