Holding trap over by Yorkshire river (6)
I believe the answer is:
tenure
'holding' is the definition.
(I've seen this before)
'trap over by yorkshire river' is the wordplay.
'trap' becomes 'net' (net is a type of trap).
'over' says the letters should be written in reverse.
'by' means one lot of letters go next to another.
'yorkshire river' becomes 'ure' (River Ure).
'net' reversed gives 'ten'.
'ten'+'ure'='TENURE'
(Other definitions for tenure that I've seen before include "Tenancy" , "Period holding office" , "Term for which to hold a position" , "Incumbency" , "Permanent employment right" .)