Neat dies I cast become rusty (7)
I believe the answer is:
oxidise
'become rusty' is the definition.
I can't judge whether this defines the answer.
'neat dies i cast' is the wordplay.
'neat' becomes 'ox' (neat historically meant a cow or ox).
'cast' indicates anagramming the letters (letters are dispersed or cast around).
'dies'+'i'='diesi'
'diesi' is an anagram of 'idise'.
'ox'+'idise'='OXIDISE'
Can you help me to learn more?
(Other definitions for oxidise that I've seen before include "Combine chemically with a particular gas - ie six do (anag)" , "Eg, rust (S, not Z)" , "Eg, go rusty" .)