Why was "tantrum" trending last week?
rounded stone with a hollow center lined with crystals, 1670s, from French géode, from Latin geodes, from Greek geodes "earthy, earth-like," from ge "earth" (Homeric gaia; see Gaia) + -oides, adjective suffix, "characterized by." Perhaps so called in reference to the "earthy" minerals inside.
geode ge·ode (jē'ōd')
A cystlike space with or without an epithelial lining, usually observed in subarticular bone in arthritic disorders.