hard as the nether millstone
(as) hard as the nether millstone
Tough or harsh and unlikely to submit. The phrase is Biblical in origin. That guy is as hard as the nether millstone—he'll never give you what you want in the negotiations.
hard as the nether millstonecallous and unyielding.
The nether millstone is the lower of the two millstones by which corn is ground. The phrase alludes to Job 41:24: ‘His heart is as firm as a stone, and as hard as a piece of the nether millstone’.