MLK's title (3)
I believe the answer is:
rev
'mlk's title' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rev that I've seen before include "Increase speed of (an engine)" , "Speed up engine (colloq.)" , "Minister" , "Clergyman, or woman (abbr)" , "Reverend (abbr.)" .)