Usage examples "keynote":
At first Ishmael, with the quick generosity of his age, had wanted to give Cloom up to his brother there and then, but the Parson talked gravely to him, impressing on him for the first time what was to be the keynote
of his teaching, that never, never must he forget that Cloom was the great trust of his life. - "Secret Bread",
F. Tennyson Jesse.
Nevertheless, as far as the doctrine of service- the serving of a cause higher than one's own self, even at the sacrifice of one's individuality; I say the doctrine of service, which is the greatest that Christ preached and is the sacred keynote
of his mission- as far as that is concerned, Bushido is based on eternal truth. - "Bushido, the Soul of Japan",
Asceticism is the keynote
of Mr. Pater's prose; at times it is almost too severe in its self- control and makes us long for a little more freedom. - "Reviews",