Definition of "hemi"

(automotive) A motor with hemispherical combustion chambers. A piston engine internal combustion engine with hemispherical piston cylinder heads.  examples

(automotive) A combustion chamber with the hemispherical cylinder head from such an engine.  examples

(automotive) A hemispherical cylinder head from such a motor.  examples

(automotive) A vehicle equipped with such a motor engine.  examples

(by extension) Domed versions of the above that have cylinder heads that are not exactly hemispherical  examples