Irons put out for use by violinists (5)
I believe the answer is:
rosin
'use by violinists' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'irons put out' is the wordplay.
'put out' indicates anagramming the letters.
'irons' is an anagram of 'ROSIN'.
'for' is the link.
Can you help me to learn more?
(Other definitions for rosin that I've seen before include "It's used on a violin bow" , "What gives bite to strings" , "No sir; it is rubbed on violin bows" , "Sticky stuff rubbed on violin strings" , "Violin bow treatment" .)