Old Tory leader in charge of hearing (4)
I believe the answer is:
otic
'hearing' is the definition.
(thesaurus)
'old tory leader in charge' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'tory leader' becomes 't' (I've seen this in other clues).
'in charge' becomes 'ic'.
'o'+'t'+'ic'='OTIC'
'of' is the link.
(Other definitions for otic that I've seen before include "of concern to the listener" , "of lugs" , "Relating to the ear" , "Listener's" , "organ" .)