Defer to old Ottoman governor (4)
I believe the answer is:
obey
'defer to' is the definition.
(thesaurus)
'old ottoman governor' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'ottoman governor' becomes 'bey' (I've seen this before).
'o'+'bey'='OBEY'
(Other definitions for obey that I've seen before include "Submit to authority" , "Carry out (an order)" , "Comply with orders" , "Carry out (a command)" , "Be ruled by" .)