Texan mission (5)
I believe the answer is:
alamo
'texan mission' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for alamo that I've seen before include "Fort in San Antonio, once famously besieged" , "Scene of massacre in Texas" , "US mission" , "Famous battle site in Texas" , "Texas mission taken by Mexican forces in 1836" .)