• (n.) The science of names or of their classification.
(on″o-mah-tol´ah-je) the science of names and nomenclature.
On`o·ma·tol'o·gy noun [ Greek ..., ... + -logy .] The science of names or of their classification. 
Onomatology is the science of names and their classification.
onomatology The study and science of names or of their classifications.