Net return on a Yorkshire river holding (6)
I believe the answer is:
tenure
'holding' is the definition.
(thesaurus)
'net return on a yorkshire river' is the wordplay.
'return' is a reversal indicator.
'on' means one lot of letters go next to another.
'a yorkshire river' becomes 'ure' (I've seen this in other clues**).
'net' in reverse letter order is 'ten'.
'ten'+'ure'='TENURE'
(Other definitions for tenure that I've seen before include "(Right of) occupancy" , "Period holding office" , "Incumbency" , "Possession of office or property" , "Retune (anag.)" .)