Sleet affected alloy (5)
I believe the answer is:
steel
'alloy' is the definition.
(I know that steel is a type of alloy)
'sleet affected' is the wordplay.
'affected' indicates an anagram.
'sleet' with letters rearranged gives 'STEEL'.
(Other definitions for steel that I've seen before include "Determination, metal" , "Hard, strong, grey alloy" , "The staying power" , "Strong metal" , "nerve" .)