Pass across eleven southern US states (5)
I believe the answer is:
dixie
'southern us states' is the definition.
(nickname for the southern US states)
'pass across eleven' is the wordplay.
'pass' becomes 'die' (as in passing away).
'across' means one lot of letters goes inside another.
'eleven' becomes 'xi' (Roman numerals).
'die' placed around 'xi' is 'DIXIE'.
(Other definitions for dixie that I've seen before include "Southern states in the American Civil War" , "The Deep South" , "Name given to southern US states" , "Seceding states" , "South America's" .)