Beware the ides of March! This much-quoted Shakespearian phrase refers to March 15th and is a classic superstition along the lines of "Don't walk under a ladder" and "Avoid suffering 13 fatal injuries." But what the heck are the ides?

The ides (falling on the 15th in months like March, and the 13th in several months) comes from the ancient Roman calendar and is considered ominous for a traditionally portentous reason: it corresponded with the full moon, which is well-known to cause werewolfism and moon madness. In Shakespeare's Julius Caesar, the lead character is given the famous warning that began this article, and he should've listened, since (spoiler alert) he was assassinated.

Caesar: What say'st thou to me now? speak once again.
Soothsayer: Beware the ides of March.

                 The Tragedy of Julius Caesar, Act I, Scene 2

Thanks to this famous use, the ides of March is the only ides anyone really cares about, which is a shame, because the ides of August are really something.

The vocabulary of time has plenty of other common and rare terms to help you navigate the space-time continuum. Here are a few timely terms that can build your vocabulary, and they're all learnable within a fortnight.

Read on, and then check out this list for more: Ides, Eon, Epoch, and Era: Time-related Words

eon
This is a length of time so long it's impossible to fathom, much less grok. The meaning of eon, a word that's been found since the 1500s, has been relatively consistent, meaning either an endless, eternity-type period of time or a geological period, which is pretty long too, involving billions of years. You're most likely to see this word in exaggerations such as "You've been yammering about Batman for eons" or "It's been eons since I went for Indian food. What's wrong with me?"

fortnight
This term meaning two weeks has been around a little longer than that, dating from the days of Old English. If you want to impress a time traveler from the days of yore, this is a great word to use. An even rarer old term, sennight, means one week.

yore
Speaking of yore, this is an old-fashioned word for old-fashioned times. "The days of yore" are the bygone, long-lost, age-old times that hardly anyone can remember but everyone loves to glorify.

halcyon
Just as people look wistfully back on days of yore, they yearn for their halcyon days, which are basically the good old days when everything was chocolate cake, everywhere and all the time. This word was originally the name of a Greek bird. As the Oxford English Dictionary (OED) puts it, a halcyon was, "A bird of which the ancients fabled that it bred about the time of the winter solstice in a nest floating on the sea, and that it charmed the wind and waves so that the sea was specially calm during the period." That's some bird, and this is some word, with a soft, lovely, lilting sound. No wonder we use it describe times that are much-missed—and times that were peaceful, relaxed, and calm. Halcyon would be a terrible word for a dumpster fire.

millenium
This word for a thousand years was heard quite frequently about 17 years ago, as we shifted from one millennium to another. By the time such a shift occurs again, we'll all be long gone, and humanity could be wiped out or perhaps relocated to a hospitable moon of Jupiter. The original meaning of this word, much like our system of years, was distinctly Christian: it referred to a foretold 1000 years in which Christ would reign on earth, according to the Book of Revelations. As words tend to do, this one changed in meaning, coming to refer to any 1000-year period. If you're setting your time machine far into the future or past, skipping past several thousand years, you're traveling through the millennia.

jubilee
A jubilee is an anniversary: usually the fiftieth anniversary. It's a celebratory, joyous, wake-the-neighbors kind of word. Originally, this was a Jewish term that is quite vividly described by the OED:  "to be proclaimed by the blast of trumpets throughout the land; during it the fields were to be left uncultivated, Hebrew slaves were to be set free, and lands and houses in the open country or unwalled towns that had been sold were to revert to their former owners or their heirs." These days, the word is far less specific, meaning pretty much any sort of celebration. Jubilee is related to jubilant, an adjective meaning happy as a clam in a bucket of ice cream. (Note to self: Check to see if ice cream actually makes clams happy.)

contemporaneous
This is a word for things that happen at the same time: if you spill apple cider on your favorite shirt while Taylor Swift is hunting rabbits in an underground maze thousands of miles beneath the Earth's surface, those events were contemporaneous. If you teach your cat to walk on a leash, and then sometime later the moon is revealed as a spy satellite for Martians, those events were non-contemporaneous. And also weird, but that's another matter.

Whether you learn these words contemporaneously or non-contemporaneously, they'll be sure to impress your friends and neighbors—especially the older ones who can't stop yakking about yore.