Slender, narrow (4)
I believe the answer is:
thin
I believe this is a double definition.
'slender' is the first definition.
(synonyms)
'narrow' is the second definition.
(similar in meaning)
(Other definitions for thin that I've seen before include "Fine" , "Spare" , "Made of light material" , "(Of smile) weak, forced" , "Unconvincing" .)