Definitions for onomasticsˌɒn əˈmæs tɪks
Random House Webster's College Dictionary
on•o•mas•tics*ˌɒn əˈmæs tɪks(n.)
the study of the origin, history, and use of proper names.
* (used with a sing. v.).
Origin of onomastics:
the branch of lexicology that studies the forms and origins of proper names
The branch of lexicology devoted to the study of names and naming, especially the origins of names.