Of delicate or slender build (6)
I believe the answer is:
svelte
'of delicate or slender build' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for svelte that I've seen before include "Slim and stylish" , "free" , "Of delicate or slender build" , "Slim and attractive" , "Polished" .)