POLYCEPHALY

[noun]

a condition of having more than one head. The term is derived from the Greek stems poly- (πολύ) meaning “much” and kephali- (κεφάλι) meaning “head”, and encompasses bicephaly and dicephaly (both referring to two-headedness). A variation is an animal born with two faces on a single head, a condition known as diprosopus. 

[Rodney Matthews]