Narrow or lean (4)
I believe the answer is:
thin
This clue is a double definition.
'narrow' is the first definition.
(associated in meaning)
'lean' is the second definition.
(I know that lean can be written as thin)
(Other definitions for thin that I've seen before include "Lean; narrow" , "Fine" , "Narrow, slim" , "Spare" , "Measure" .)