quindenary

Etymology
From.

Adjective

 * 1) Containing fifteen things, or to the base of fifteen.
 * 2) * 1878, James Joseph Sylvester, On an Applicaton of the New Atomic Theory, etc, appendix 1, Remarks on Differentiants expressed in terms of the differences of the roots of their parent quantics, originally published in the American Journal of Mathematics, republished in The Collected Mathematical Papers of James Joseph Sylvester (2008, ISBN 0821847201, page 170:
 * it and M. Hermite's form ; the latter is intrinsically a quinary group of triadic products, but such representation in the case of M. Joubert's form is purely conventional and confusing, it really being a single indecomposable quindenary product.