You must remember this (5)
I believe the answer is:
alamo
'you must remember this' 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 "Scene of massacre in Texas" , "The red planet" , "Site of a Texas siege, 1836" , "Where Davy Crockett met his end" , "Davy Crockett's last stand" .)