Calmer, I arranged amazing event (7)
I believe the answer is:
miracle
'amazing event' is the definition.
(I've seen this before)
'calmer i arranged' is the wordplay.
'arranged' indicates an anagram (letters rearranged).
'calmer'+'i'='calmeri'
'calmeri' is an anagram of 'MIRACLE'.
(Other definitions for miracle that I've seen before include "Supernatural occurrence" , "astonishing feat" , "Extraordinary event" , "Marvel" , "Inexplicable wonder" .)