Right to ring ambassador for an explanation (6)
I believe the answer is:
theory
'an explanation' is the definition.
(thesaurus)
'right to ring ambassador' is the wordplay.
'right' becomes 'tory' (I've seen this before).
'to ring' is an insertion indicator.
'ambassador' becomes 'he' (His or Her Excellency).
'tory' placed around 'he' is 'THEORY'.
'for' acts as a link.
(Other definitions for theory that I've seen before include "General principle which explains some aspect of the world" , "Supposition, set of ideas" , "Hypothetical reasoning" , "Scientific conjecture" , "Justifying hypothesis" .)