keynote
[noun]
Synonyms: heart, centre, core, essence, gist, substance, theme

[TahlilGaran] English Synonym Dictionary ▲

I. key‧note¹ /ˈkiːnəʊt $ -noʊt/ noun [countable]
the main point in a book, system of beliefs, activity etc that influences everything else
keynote of
Unprecedented change has been the keynote of the electronic revolution.

[TahlilGaran] Dictionary of Contemporary English ▲

II. keynote² adjective [only before noun]
relating to the most important part of a formal meeting, report etc
keynote speech/address/lecture etc
He is scheduled to deliver the keynote address at an awards ceremony.
Bill Gates is booked as the keynote speaker.

[TahlilGaran] Dictionary of Contemporary English ▲

III. keynote³ verb [intransitive and transitive]
to give the keynote speech at a formal meeting, ceremony etc:
The event is usually keynoted by the prime minister.

[TahlilGaran] Dictionary of Contemporary English ▲