Mogul governor in Washington wearing collar (5)
I believe the answer is:
nawab
'mogul governor' is the definition.
(I've seen this in another clue)
'washington wearing collar' is the wordplay.
'washington' becomes 'wa' (two letter abbreviation for the state).
'wearing' means one lot of letters goes inside another.
'collar' becomes 'nab' (both can mean to catch a person).
'wa' inserted within 'nab' is 'NAWAB'.
'in' acts as a link.
(Other definitions for nawab that I've seen before include "Indian governor" , "Muslim prince in India" , "Governor in Mogul empire" , "Important Muslim" , "Indian ruler" .)