England's highest military man? (6)
I believe the answer is:
nelson
'military man?' is the definition.
(Lord Nelson)
I cannot understand how the remainder of the clue works.
(Other definitions for nelson that I've seen before include "northern town" , "... famous admiral" , "Naval hero, d. 21 October 1805" , "Lady Hamilton's admiral lover" , "'Horatio ..., English admiral (6)'" .)