Weird Words of Science 5 from chemistry notes

secular If you look up secular in most dictionaries, the only definition given is "non-religious" or "of the world". Hunting a bit deeper yields an astronomical meaning, coming from Roman usage where a secular event is one that happens once in long period (such as century). [The Latin root is saeculum, "age".] Astronomers refer to long-period effects as "secular" effects. The secular effects in an orbit can be found by finding the roots of the secular determinant, which has the same form as the determinant that arises in quantum mechanics' linear variation theory. The physicists working on linear variation theory noticed the similarity in form and used the same term.