Greek hepta, seven.
A heptagon is a plane figure with seven sides; a heptahedron is a solid one with seven faces. A heptarchy (Greek arkhia, rule) is a state or region consisting of seven smaller, autonomous regions, or government by seven rulers; a heptathlon (Greek athlon, contest) is an athletics contest in which competitors take part in a set of seven events. Heptachlor is a chlorinated hydrocarbon used as an insecticide whose molecule contains seven chlorine atoms; the heptoses are a group of sugars whose molecules each contain seven carbon atoms. See also septi‑.