keynote

The tonic of a musical key.

A prime underlying element or theme.

To give or set the keynote of.

To give a keynote address at.

In music, the tone on which a key (tonality) is founded; a tonic. See key, 7 .

A central principle or idea; the pivotal point in a system, a composition, or a course of action; a controlling thought.

The tonic or first tone of the scale in which a piece or passage is written; the fundamental tone of the chord, to which all the modulations of the piece are referred; — called also key tone.

The fundamental fact or idea; that which gives the key.

The note on which a musical key is based.

The main theme of a speech, a written work, or a conference.