bone dry
Extremely dry. Man, it is bone dry out there today—not a bit of humidity in the air. And if that floor is anything less than bone dry when you're done, make sure to put up the signs—we don't need anyone slipping out here!
bone dry
Very thirsty; extremely dry. The simile dry as bone, referring to the bones of a dead creature, dates from the sixteenth century and has survived to the present day, while others of the same period (dry as a sieve, dry as a chip, dry as a red herring) have long since died out. See also dry as dust.