Feats carried out with unknown security (6)
I believe the answer is:
safety
'security' is the definition.
(thesaurus)
'feats carried out with unknown' is the wordplay.
I cannot really see how this works, but
an anagram of 'feats' is 'safet' which is within the answer.
'unknown' could be 'y' (algebra) and 'y' is found in the answer.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for safety that I've seen before include "Absence of danger" , "Motto of the cautious!" , "Freedom from risk or danger, or an acrobat's net" , "Sort of catch" , "one finds in numbers" .)