Tombstone lawman (4)
I believe the answer is:
earp
'tombstone lawman' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for earp that I've seen before include "Wyatt -, renowned US lawman" , "Wyatt - - (US marshal)" , "See 4 Across" , "Wyatt --, US law officer" , "Wyatt - (O.K. Corral)" .)