Definition - The study of proper names and their origins.

1. As opposed to onomatology, the science of the formation of names and terms, and onomasiology, the study of common names — specifically, the principles of naming, especially regarding regional, social, and occupational variations.
2. The branch of onomastics that studies human names is called anthroponymy.

Etymology -
The word derives from the Greek onomastikos, of or belonging to naming (from onoma, name).

Oxford English Dictionary -
Its first citation in this sense is from 1930:
"The man learned in sciences, in onomastic." [sic]
(T. S. Eliot tr. St.-J. Perse's Anabasis x. 67)

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