Small, delicate and mostly finely structured (5)
I believe the answer is:
elfin
'small delicate' is the definition.
(elfin means small and delicate)
'mostly finely structured' is the wordplay.
'mostly' means to remove the last letter.
'structured' is an anagram indicator.
'finely' with its final letter taken off is 'finel'.
'finel' with letters rearranged gives 'ELFIN'.
'and' is the link.
(Other definitions for elfin that I've seen before include "Small, delicate, mischievous and attractive" , "Spritely" , "Fairy-like" , "Petite and charming" , "Pixie-like" .)