Free - and terribly secure! (6)
I believe the answer is:
rescue
'free' is the definition.
(I've seen this in another clue)
'terribly secure' is the wordplay.
'terribly' is an anagram indicator.
'secure' is an anagram of 'RESCUE'.
'and' acts as a link.
(Other definitions for rescue that I've seen before include "Get over, on top of" , "Free someone from trouble" , "Being presumptuous" , "liberation" , "Help out of difficulty, save" .)