Layer, level (4)
I believe the answer is:
tier
I believe this is a double definition.
'layer' is the first definition.
(I know that tier is a type of layer)
'level' is the second definition.
(I know that level can be written as tier)
(Other definitions for tier that I've seen before include "one doing Bond" , "Rank - row" , "Row in theatre" , "Person joining" , "Layer, rank" .)