Notes that don't agree (7)

I believe the answer is:

discord

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'agree' is the definition.
The definition and answer can be both to do with fundamental existence as well as being verbs in their base form.
Perhaps they are linked in a way I don't understand?

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for discord that I've seen before include "Friction" , "Disagreement" , "contention" , "Strife, lack of harmony" , "Dissension" .)

I've seen this clue in The Globe and Mail.

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