Frankness can upset the nosy (7)
I believe the answer is:
honesty
'frankness' is the definition.
(I've seen this in another clue)
'upset the nosy' is the wordplay.
'upset' is an anagram indicator.
'the'+'nosy'='thenosy'
'thenosy' is an anagram of 'HONESTY'.
'can' is the link.
(Other definitions for honesty that I've seen before include "Straightforwardness" , "Fairness" , "Uprightness" , "Integrity" , "Probity; plant" .)