Layer (4)
'layer' is the definition.
(I know that tier is a type of layer)
This is the entire clue.
(Other definitions for tier that I've seen before include "One of two or more rows" , "Echelon" , "Plague" , "One who secures" , "Layer, rank" .)
'layer' is the definition.
(I know that ply is a type of layer)
This is the entire clue.
(Other definitions for ply that I've seen before include "Thickness of yarn and wood" , "Fold; thickness" , "drama one's missed" , "This wood is laminated" , "Work steadily as at one's trade" .)
'layer' is the definition.
(I know that layer can be written as stratum)
This is all the clue.
(Other definitions for stratum that I've seen before include "Social class - level" , "Bed of sedimentary rock" , "Layer (of rock)" , "stretch of rock" , "(Geological) layer" .)
'layer' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for sheet that I've seen before include "Piece of paper; nautical rope" , "Piece of linen; ship's rope" , "Sail-rope on the bed?" , "Whence to sing hymns?" , "Mattress cover" .)
(Other definitions for ozone that I've seen before include "Shield against radiation" , "Kind of oxygen layer in atmosphere, has hole in it" , "Bracing air (colloq.)" , "Colourless gas soluble in alkalis and cold water" , "Atmospheric gas shielding us from ultraviolet radiation" .)