Definition of nomen novum:
(N) :
In biological nomenclature, a nomen novum (Latin for "new name"), new replacement name (or replacement name, new substitute name, substitute namehttp://www.iczn.org/iczn/index.jsp ICZN Code (Glossary)) is a scientific name that is created specifically to replace another scientific name, but only when this other name cannot be used for technical, nomenclatural reasons (for example because it is a homonym: it is spelled the same as an existing, older name).