[xml-dev] Where does the term "element" come from?

Most likely from 'data element'.

Several decades ago the predominant programming languages included 
FORTRAN, COBOL, ALGOL and PL/I. Applications typically operated with an 
ad hoc data store. For file-oriented input (as opposed to streams),  
programming specifications typically included a record layout, showing 
the fields or data elements that comprised a record. When projects were 
done with programming teams, a data dictionary was used to ensure 
consistency of the data elements (size, type, location in a record).

With the emergence of record management sytems (e.g. DEC RMS) and 
databases, applications written in different languages could access the 
same data on disk. There was a need for tools to ensure consistency of 
the definition of data elements across projects and programming 
languages.

Common Data Dictionary software, repository-based design, data modeling 
software and other CASE tools emerged as solutions.