What's a keynote?

–noun 1. Music. the note or tone on which a key or system of tones is founded; the tonic.

2. the main idea or central principle of a speech, program, thought, action, etc.

3. the policy line to be followed, as by a party in a political campaign, that is set forth authoritatively in advance by an address or other formal announcement.

4. keynote address.

–verb (used with object) 5. to announce the policy of (a political party, campaign, assembly, etc.); deliver a keynote address at: The governor will keynote the convention.

6. to serve as the keynote for.

7. Music. to give the keynote of.

–verb (used without object) 8. to provide a keynote, esp. a keynote address: He refused an invitation to keynote.

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[Origin: 1755–65; key1 + note]

It depends on the context it is being used in . . . in music it means the note or tone on which a key or system of tones is founded. In general it can mean the main idea or central principle of a speech, program, thought, action, etc. It can also mean the policy line to be followed, as by a party in a political campaign, that is set forth authoritatively in advance by an address or other formal announcement.