Clathrate

A clathrate is a complex of molecules forming a cage enclosing a guest molecule (though clathrates without a guest molecule have been synthesised). The word is from the Greek klathron, meaning enclosed.

The most well known clathrate is methane hydrate which has methane as the guest molecule. This "burning ice" (when it releases its flammable methane) is only stable at high pressures. Stocks of it are deeply buried in the subsoil, particularly under the ocean beds.