Key·note n.
 1. Mus. 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.
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 Key tone n. Mus. See Keynote.
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