Gay Prince ruined the eulogy (9)
I believe the answer is:
panegyric
'the eulogy' is the definition.
('panegyric' can be a synonym of 'eulogy')
'gay prince ruined' is the wordplay.
'ruined' is an anagram indicator.
'gay'+'prince'='gayprince'
'gayprince' with letters rearranged gives 'PANEGYRIC'.
(Other definitions for panegyric that I've seen before include "Speech or piece of writing praising person" , "Eulogy" , "Speech of praise" , "words of tribute" , "Laudatory address" .)