Keynote (noun)

1. A speech or presentation that sets the tone or theme for a conference, meeting, or event.
2. A main or central idea or principle that underlies or is emphasized in a speech, presentation, or work of art.
3. The main melody or theme in music.

Origin:

The word 'keynote' originated from the musical term meaning 'the tonic or principal note in a key'.

Examples:

1. The keynote speaker at the conference gave a powerful and inspiring address.
2. The keynote address set the tone for the rest of the conference, outlining the main goals and objectives.
3. The keynote of the symphony was a beautiful and intricate melody.
4. The keynote of the painting was a vivid and bold use of color.
5. The keynote of the film was a message of hope and perseverance.