Streamlined changes are nothing energetic (11)
I believe the answer is:
aerodynamic
'streamlined' is the definition.
(streamlined for travel through air)
'changes are nothing energetic' is the wordplay.
'changes' indicates an anagram.
'nothing' becomes 'O' (O resembles 0).
'energetic' becomes 'dynamic' (associated in meaning).
'are' is an anagram of 'aer'.
'aer'+'o'+'dynamic'='AERODYNAMIC'
(Other definitions for aerodynamic that I've seen before include "could be made to fly?" , "Fit to be a high-flyer" , "very good on air?" , "Designed like a bird" , "Streamlined" .)