Rare butterfly effect's start around butterfly's opening (9)
I believe the answer is:
admirable
'rare' is the definition.
(thesaurus)
'butterfly effect's start around butterfly's opening' is the wordplay.
'butterfly' becomes 'admiral' (admiral is a kind of butterfly**).
'start' indicates taking the first letters.
'around' indicates putting letters inside.
'opening' suggests taking the first letters.
The initial letter of 'effects' is 'e'.
The first letter of 'butterflys' is 'b'.
'admiral'+'e'='admirale'
'admirale' enclosing 'b' is 'ADMIRABLE'.
(Other definitions for admirable that I've seen before include "Splendid" , "Excellent" , "Praiseworthy" , "Commendable" , "Very well regarded" .)