One irreducible part of a larger whole. An element is chosen as a stopping point, not found as one.
Latin elementum (a first principle, a rudiment), a word whose own origin is disputed, possibly from the letters l, m, n once recited together as a teaching aid.
One account of its own root is almost too fitting: elementum may come from L, M, N, three letters once recited together as a child's first lesson in the alphabet. Whether or not that story is true, an element is still exactly that kind of stopping point, chosen for teaching rather than discovered as a fact of nature.