'Unnatural' in the Bible

For this reason God gave them over to degrading and vile passions; for their women exchanged the natural function for that which is unnatural [a function contrary to nature],

just as Sodom and Gomorrah and the adjacent cities, since they in the same way as these angels indulged in gross immoral freedom and unnatural vice and sensual perversity. They are exhibited [in plain sight] as an example in undergoing the punishment of everlasting fire.