I am confused how fugio is used grammatically when it is used idiomatically to mean forget. In Latin the regular word for forget is dedisco (to unlearn). However, usually the Latins used various idioms to capture this meaning. For example, the word obliviscor (to darken) is used sometimes to mean forget, the idiom being that the "mind darkens". Another word that is used is praetereo (to pass by), the idea being that the mind "passes by" or overlooks something. However, probably the most common idiom used to mean forget was fugio (to flee). So, for example, we have this statement by Macrobius:
Hunc ergo ordinem Romanis quoque imitari placuit, sed frustra, quippe fugit eos deum unum, sicut admonuimus, additum a se Graecum numerum in honorem imparis numeri.
(Therefore, it pleased the Romans to imitate this system, but in vain, because of course they forgot the one day added to the Greek count by themselves in honor of the odd number, as we mentioned above.)
I don't quite understand the grammar of this, specifically where it says fugit eos deum unum. The first part apparently means (it) fled them, meaning they forgot, where eos refers to Romanis. But of what is deum unum the object of? It is in the accusative, so it is clearly meant to be an object, but there is no verb of which it is an object. Is the idea that there is an imaginary word "forget" and deum unum is the object of that imaginary word? In other words, the idiom, fugit eos, could be thought of as being the same as dedidicērunt. So, the analogy is that we can read the phrase instead as:
quippe deum unum dedidicērunt additum a se Graecum numerum ....
So, essentially there are two accusatives in the phrase, eos, which is the object of fugit, and deum unum, which is the object of the entire idiom <fugit eos>. Is that the way to understand it?