Elementary a. : Having only one principle or constituent part; consisting of a single element; simple; uncompounded; as, an elementary substance.

Elementary a. : Pertaining to, or treating of, the elements, rudiments, or first principles of anything; initial; rudimental; introductory; as, an elementary treatise.

Elementary a. : Pertaining to one of the four elements, air, water, earth, fire.

Example:
What is the smallest Elementary particle?

Taxonomy
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Defination from the web:
Elementary algebra is the most basic form of algebra taught to students who are presumed to have no knowledge of mathematics beyond the basic principles of arithmetic. In computational complexity theory, the complexity class ELEMENTARY is the union of the classes in the exponential hierarchy. ...