It's applied to violin strings and possibly irons (5)
I believe the answer is:
rosin
'it's applied to violin strings' is the definition.
I can't tell whether this definition defines the answer.
'possibly irons' is the wordplay.
'possibly' indicates an anagram.
'irons' with letters rearranged gives 'ROSIN'.
'and' is the link.
Can you help me to learn more?
(Other definitions for rosin that I've seen before include "Colophony" , "Sticky stuff rubbed on violin strings" , "Varnish etc. from turpentine" , "Rub it along the violin bow" , "Violin bow treatment" .)