Row over new material (5)
I believe the answer is:
linen
'material' is the definition.
(linen is a kind of material)
'row over new' is the wordplay.
'row' becomes 'line' (I've seen this before).
'over' says to put letters next to each other.
'new' becomes 'n'.
'line'+'n'='LINEN'
(Other definitions for linen that I've seen before include "Spun fibres of flax" , "Flax textile" , "E.g. bedclothes" , "Cloth woven flax fibres" , "sheets, perhaps" .)