Small arch (5)
I believe the answer is:
elfin
I believe this is a double definition.
'small' is the first definition.
(similar in meaning)
'arch' is the second definition.
(thesaurus)
(Other definitions for elfin that I've seen before include "Like a little fairy" , "Fairy-like" , "Sprightly" , "Petite and charming" , "Pixie-like" .)