The study of proper names or of terms used in a specialized field.

Okay--how is this different from jargon?

how is this different from jargon?

Onomastics (as its name implies) deals with proper names. Jargon is a specialize vocabulary use in a field. It may include some proper names, but also other non-name words.

but, if Anu's def'n is correct, onomastics includes jargon.

here's a broader effort, from W3:

1 a : the science or study of the origins and forms of words especially as used in a specialized field (as science or commerce) b : the science or study of the origin and forms of proper names of persons or places [any student of onomastics and of surnames in particular -- Otto Springer]
2 : the system underlying the formation and use of words especially for proper names or of words used in a specialized field [according to rules of Indo-European onomastics -- E.E.Herzfeld]

all squares are rectangles, but not all rectangles are squares.

Jargon is applied to a technical or esoteric language used by a profession, trade, or cult.

Example: Educationese is the jargon of educational theorists.

Hey, Mongoose, welcome