Palladium, introducing old character, cut back (6)
I believe the answer is:
pruned
'cut back' is the definition.
'palladium introducing old character' is the wordplay.
'palladium' becomes 'pd' (Pd is the chemical symbol for palladium).
'introducing' indicates putting letters inside (some letters introduced or inserted into others).
'old character' becomes 'rune' (rune is a kind of character. I am not sure about the 'old' bit.**).
'pd' enclosing 'rune' is 'PRUNED'.
(Other definitions for pruned that I've seen before include "Cut away overgrown branches" , "what one did making Bush appear smart?" , "reduced to a minimum?" , "(Of a shrub) cut back" , "Trimmed by cutting away roots and branches to promote growth" .)