Decoration for eccentric and mentor (9)
I believe the answer is:
adornment
'decoration' is the definition.
(adornment is a kind of decoration)
'eccentric and mentor' is the wordplay.
'eccentric' is an anagram indicator.
'and'+'mentor'='andmentor'
'andmentor' anagrammed gives 'ADORNMENT'.
'for' acts as a link.
(Other definitions for adornment that I've seen before include "form of beautification?" , "decking" , "Embellishment" , "Ornamentation" , "decorating" .)