keynote

Short definition from Wiktionary

Noun

1. 1
   A speech that sets the main theme of a conference or other gathering; a keynote speech or keynote address.
2. 2
   The main theme of a speech, a written work, or a conference.
3. 3
   The note on which a musical key is based; the tonic.

Verb

1. 1
   To deliver a speech that sets the main theme of a conference or other gathering.