Means of escape secured by adventurer (4)
I believe the answer is:
vent
'means of escape' is the definition.
(I've seen this in another clue)
'secured by adventurer' is the wordplay.
'secured by' says the answer is hidden in the clue (the solution is secured within the clue).
'VENT' is hidden within 'adventurer'.
(Other definitions for vent that I've seen before include "Give free expression to -- opening" , "pipe" , "Opening; release (fluid)" , "Air passage" , "Small outlet" .)