Stirring up old men, the writer Voltaire, say (3,2,5)
I believe the answer is:
nom de plume
'voltaire say' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'stirring up old men the writer' is the wordplay.
'stirring' is an anagram indicator.
'the writer' becomes 'me' (the person who wrote the clues).
'up'+'old'+'men'='upoldmen'
'upoldmen' with letters rearranged gives 'nomdeplu'.
'nomdeplu'+'me'='NOM DE PLUME'
Can you help me to learn more?
(Other definitions for nom de plume that I've seen before include "Pen-name" , "Soubriquet" , "Assumed name" , "False name" , "Literary pseudonym" .)