Bust out (6)
I believe the answer is:
escape
'bust out' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for escape that I've seen before include "Abscond, flee" , "A key at top, on left" , "performance by Houdini?" , "Break loose, get away" , "'Break free, get away (6)'" .)