*(s)teg-

The core idea of this root was:

covering

This idea is pretty well preserved in most of its relatives. In the Germanic branch we have the German Decke (cover, ceiling) and the English thatch and deck (which originally was a “cover” of the ship).
On the Latin side of the family tree, there was the verb *tegere, which pretty much meant to cover, to give roof and which is the origin of protect (add cover), detect (remove cover) and tile and its German cousin Ziegel, which both originally meant “roof tile”.
Honorable mention to the epic Stegosaurus. That beast got its name from the big bone plate “covering” his head. So basically, it’s called “roof-lizzard” … yeah, not as epic as the Latin name.