Docile nun remarkably ecstatic on this (5,4)
I believe the answer is:
cloud nine
'ecstatic on this' is the definition.
(an ecstatic person is said to be on cloud nine)
'docile nun remarkably' is the wordplay.
'remarkably' is an anagram indicator.
'docile'+'nun'='docilenun'
'docilenun' with letters rearranged gives 'CLOUD-NINE'.
(Other definitions for cloud nine that I've seen before include "On which one is blissfully happy" , "On this, one is extremely happy" , "If you're on this, you're extremely happy" , "Situation of great elation" .)