Old provincial governor finally senses an ambush (6)
I believe the answer is:
satrap
'old provincial governor' is the definition.
(term for a governor in various ancient empires)
'finally senses an ambush' is the wordplay.
'finally' indicates one should take the final letters.
'an' becomes 'a'.
'ambush' becomes 'trap' (synonyms).
The last letter of 'senses' is 's'.
's'+'a'+'trap'='SATRAP'
(Other definitions for satrap that I've seen before include "Old Persian governor - a sprat (anag)" , "A sprat for the old governor of Persia" , "Old Persian governor took a seat to start" , "Old head" , "Raps at the governor in ancient Persia" .)