Tetra-, [Gr. te`tra-, from te`sares, te`ttares, four. See Four.].
A combining form or prefix signifying four, as in tetrabasic, tetrapetalous. [1913 Webster]
A combining form (also used adjectively) denoting four proportional or combining parts of the substance or ingredient denoted by the term to which it is prefixed, as in tetra-chloride, tetroxide. [1913 Webster]