Nearly all with a second mission (5)
I believe the answer is:
alamo
'mission' is the definition.
(famous mission and siege from the Texas revolution)
'nearly all with a second' is the wordplay.
'nearly all' becomes 'al'.
'with' says to put letters next to each other.
'second' becomes 'mo' (both are short periods of time).
'al'+'a'+'mo'='ALAMO'
(Other definitions for alamo that I've seen before include "national monument" , "Scene of massacre in Texas" , "Site of 1836 massacre in Texas" , "ill-fated mission" , "1836 massacre at a San Antonio, Texas mission" .)