Keynote
Pronunciation : Key"note`
Part of Speech : n.
Definition : 1. (Mus.)
Defn: 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.
2. The fundamental fact or idea; that which gives the key; as, the keynote of a policy or a sermon.
Source : Webster's Unabridged Dictionary, 1913