www.alphadictionary.com

For some reason, mainly the daily influence of this forum, I keep paying attention to etymology of the words I encounter. Thus it was in browsing the NYT today, I came across the word "cusp." Now I first remember meeting that word in Heinlein's Stranger in a Strange Land, and I had thought he had made it up. Not so. Astronomers used the term as early as 1580 to refer to the points of a crescent moon. Derives from Latin for the point of a spear. It can also refer to the point of a tooth, so I'm pretty sure it is hidden in "bicuspid."

I do think the dictionary does not point out the most frequent use I find, the sense of a turning point or a critical point in decision making.

It's also used in astrology, as in born on the cusp of a sign.

Pseudosciences such as astrology can use scientific words like cusp. Just like using angst makes psychiatry, another pseudoscience, look scientific.