Part of threat on a link having no established key (6)
I believe the answer is:
atonal
'no established key' is the definition.
Both the answer and definition are adjectives. Maybe you can see an association between them that I can't see?
'part of threat on a link' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'ATONAL' can be found hidden inside 'threat on a link'.
'having' is the link.
Can you help me to learn more?
(Other definitions for atonal that I've seen before include "(Of music) without key" , "(Music) having no established key" , "(Of music) lacking key" , "Keyless" , "Lacking traditional musical tone structure" .)