caloo_calay's definitions

harder than nails

Wood hardens with age. After a period of time, you can't drive nails in some types. A carpenter might call such wood "harder than nails".

The term could be applied to many other materials that harden with age, often as an exaggeration; often food.

hard, stale, inedible

Those left-over biscuits are harder than nails.

by caloo_calay December 2, 2013