Smooth emerald isn’t warped (11)
I believe the answer is:
streamlined
'smooth' is the definition.
(thesaurus)
'emerald isn't warped' is the wordplay.
'warped' indicates anagramming the letters.
'emerald'+'isnt'='emeraldisnt'
'emeraldisnt' anagrammed gives 'STREAMLINED'.
(Other definitions for streamlined that I've seen before include "Shaped for speed" , "Designed to reduce wind resistance" , "Designed for smooth flow" , "Of sleek appearance" , "made more efficient" .)