Eccentric don put on black tie (4)
I believe the answer is:
bond
'tie' is the definition.
(bonding is a kind of tiing)
'eccentric don put on black' is the wordplay.
'eccentric' indicates an anagram.
'put on' is a charade indicator (letters next to each other).
'black' becomes 'b' (as in pencil classifications).
'don' with letters rearranged gives 'ond'.
'ond' after 'b' is 'BOND'.
(Other definitions for bond that I've seen before include "Join; secret agent" , "Tie - debenture" , "Fictional agent; link" , "Certificate of debt" , "Financial asset" .)