Covering a fifty year arrangement? (5)
I believe the answer is:
layer
'covering' is the definition.
(a layer is covering)
'a fifty year arrangement?' is the wordplay.
'a fifty' becomes 'l' (Roman numeral).
'arrangement?' indicates an anagram (I've seen 'arrangement' mean this).
'year' with letters rearranged gives 'ayer'.
'l'+'ayer'='LAYER'
(Other definitions for layer that I've seen before include "plate?" , "Lamina" , "One supplying eggs" , "Blanket - single thickness" , "Stratum or thickness" .)