Old man, leader of Hallé and American orchestra (7)
I believe the answer is:
husband
'old man' is the definition.
(thesaurus)
'leader of halle and american orchestra' is the wordplay.
'leader of' says to take the initial letters.
'and' is a charade indicator (letters next to each other).
'american' becomes 'us'.
'orchestra' becomes 'band' (I've seen this before).
The initial letter of 'halle' is 'h'.
'h'+'us'+'band'='HUSBAND'
(Other definitions for husband that I've seen before include "Man United" , "Spouse - save" , "Consort" , "Conserve" , "Use resources economically" .)