Layer, row (4)
I believe the answer is:
tier
I believe this clue is a double definition.
'layer' is the first definition.
(I know that tier is a type of layer)
'row' is the second definition.
(a tier is a row of things)
(Other definitions for tier that I've seen before include "I might draw" , "Level of a structure" , "One making knot - level" , "Plague" , "Row (of seats)" .)