milk of human kindness, the

Compassion, sympathy, as in There's no milk of human kindness in that girl—she's totally selfish. This expression was invented by Shakespeare in Macbeth (1:5), where Lady Macbeth complains that her husband “is too full of the milk of human kindness” to kill his rivals.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.