Diplomatic mission of a head of government in a state of elation (8)
I believe the answer is:
legation
'diplomatic mission' is the definition.
(legation is a kind of diplomatic mission)
'head of government in a state of elation' is the wordplay.
I cannot really see how this works, but
'government' could be 'g' (abbreviation for government) and 'g' is present in the answer.
an anagram of 'elation' is 'leation' which is located in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
'of a' acts as a link.
Can you help me to learn more?
(Other definitions for legation that I've seen before include "Diplomatic minister and staff, and their residence" , "Embassy" , "A long tie (anag.)" , "Diplomatic group or mission" , "Official residence of diplomat and staff" .)