The Great Seal of the United States was designed in stages, first by three comittes, and then by two individual designers: Charles Thomson and then William Barton. Of particular interest is the contributions added by Charles Thomson. He is the one who added the motto to the inverse, "Novus Ordo Seclorum".
So many people desperately want this to mean, "New World Order". Charles Thomson says he intended, "...and the words under it signify the beginning of the new American Æra, which commences from that date." Thomson, being one of Them, some say, is just hiding the true meaning. The global conspiracy requires Them to announce their intentions, but they don't have to admit it, after all.
The situation should be easy to resolve. What does Novus Ordo Seclorum actually mean? novus is easy: it's a nominative adjective modifying the nominative singular ordo. Novus is 'new'; ordo is 'order', less strongly 'row, regular pattern, rank'. Novus ordo is 'new order'. The sticking point is seclorum.
A good Latin dictionary will tell you that seclorun is the genetive plural of saeculum. means 'age' or 'era', or possibly 'generation' or 'century'. The Roman aping of the Greek Olympic games were the ludi saeculares, the secular games, or the games of the age.
However, one authority I spoke to wanted to translate 'seclorum' as 'world'. 'saeculum' is after all, the root for the English 'secular' which means 'the material world', right? This is an artifact of Medieval philosophy: God is infinite, and perfect, and therefore timeless. He is removed from the material world, which is finite, imperfect, and obeys the passage of time (bonus points for anyone who sees the influence of Zoroastrian, synecretic, or even Cathar thought here.) Therefore anything that has to do with the material world and it's eras is not godly. Therfore, 'secular' is opposed to 'divine'.
Oops. That's the English word 'secular', not the Latin saeculum. Even if saeculum meant the same thing as 'secular', 'secular' is better understood as 'worldly' not 'world'. Novus Ordo Seclorum would be 'new worldly order'.
Oops. Except that that nasty seclorum is a genetive plural noun. Which means it means 'of the ____s'. Grammatically, 'worldly' is an adjective. 'New Order of the Worldlies'* makes no sense in English. 'Ages' just works better.
What if They really meant to say 'New World Order'? There are many, many better ways to pull that off. Terra is 'Earth, dirt, the world'. The Romans named the sea at the center of their world the Mediterranean after all. Orbis is 'globe' or 'sphere'; that fits our modern cosmology - something They ought to have known about back in 1782. Patriae would be more of a stretch: patria is 'fatherland' or 'nation'. Novus Ordo Patriarum would be 'new order of the nations'. Novus Ordo Terrae, Novus Ordo Orbis or Novus Ordo Patriarum then. But not Novus Ordo Seclorum. That just means 'new order of the ages', just like Mr. Thomson imagined.
Drat. They win again.