Earl and headless monster going out (6)
I believe the answer is:
egress
'going out' is the definition.
(act of exiting)
'earl and headless monster' is the wordplay.
'earl' becomes 'e'.
'and' says to put letters next to each other.
'headless' means to remove the first letter.
'monster' becomes 'ogress' (female ogre).
'ogress' with its first letter removed is 'gress'.
'e'+'gress'='EGRESS'
(Other definitions for egress that I've seen before include "Way out; going out" , "Way out or means of exit" , "Emergence, coming out" , "At the right moment" , "Way out, departure" .)