The last sort of word to define secrecy (7)
I believe the answer is:
stealth
'word to define secrecy' is the definition.
(I've seen this before)
'the last sort' is the wordplay.
'sort' indicates anagramming the letters.
'the'+'last'='thelast'
'thelast' is an anagram of 'STEALTH'.
'of' acts as a link.
(Other definitions for stealth that I've seen before include "Cats display this" , "Avoidance of detection by moving carefully" , "Halt set in furtive manner" , "word to define secrecy" , "Skill in furtive activity" .)