Cartilage; now especially: cartilage present, as a tough substance, in meat.
(figuratively, from obsolete scientific theory) Bone not yet hardened by age and hard work.
1885, Ada Sarah Ballin, The Science of Dress in Theory and Practice,
It. must be borne in mind that the bones of a young infant are little more than gristle, and are liable to bend, and so become deformed.