Cartilaginous (pronounced car-tuh-LAJ-in-us) describes something made of cartilage, the tough, flexible tissue that gives structure to parts of your body without being as hard as bone. Your ears and nose are cartilaginous: bend your ear forward and notice how it springs back. That bendable firmness is cartilage at work.

In science class, you'll encounter this word most often when learning about cartilaginous fish like sharks, rays, and skates. Unlike salmon or goldfish, which have bony skeletons, sharks have skeletons made entirely of cartilage. This makes them lighter and more flexible in the water, letting them twist and turn with incredible agility.

Cartilage appears throughout your own body too. It cushions the joints between your bones, forms the structure of your windpipe, and connects your ribs to your breastbone. Before you were born, much of your skeleton started as cartilage and gradually hardened into bone as you grew. Some of it stayed cartilaginous, like the tip of your nose and the flexible parts of your ribs that let your chest expand when you breathe deeply.