Frank J. Wilstach, comp. A Dictionary of Similes. 1916.

Demure

Demure as a cat.
—Anonymous

Demure as a nun.
—Anonymous

Demure as a Quaker.
—Anonymous

Demurely as a judge that pronounceth sentence of death.
—John Ford

As demure as if butter would not melt in his mouth.
—John Ray (Handbook of Proverbs, 1670)