Unusual hex not fully broken by spies (7)
I believe the answer is:
special
'unusual' is the definition.
(I've seen this before)
'hex not fully broken by spies' is the wordplay.
'hex' becomes 'spell' (spelling is a kind of hexing).
'not fully' means to remove the last letter.
'broken by' indicates putting letters inside (inserted letters break into the word).
'spies' becomes 'CIA' (Central Intelligence Agency).
'spell' with its last letter removed is 'spel'.
'spel' enclosing 'cia' is 'SPECIAL'.
(Other definitions for special that I've seen before include "Exceptional in intensity or quality" , "Rare, valuable" , "Bargain" , "Dish not on main menu" , "Day's non-menu dish" .)