According to the OED, the word effront is a backformation from effronted (which used to be an English word) and means:
- To free from bashfulness,
- To put to confusion.
In the 1911 Webster's dictionary on Google books, I find the second definition, as well as:
- To give assurance to.
The verb effront is incredibly rare; nearly all the hits in Google books are misspellings of affront. I suspect that it has mainly been used by people who guessed at its meaning by knowing the meaning of the adjective effronted, and not by people who learned its meaning from hearing or reading it.
The word effronted used to be a real English word, and according to the OED it means:
Shameless, barefaced, unblushingly insolent.
So what would effront mean, if it's a backformation from effronted? It's what you have to do to somebody to make them effronted. What would do this isn't clear at all.
So would all three definitions of effront above, if done to somebody, result in them being shameless, barefaced, unblushingly insolent?
I think so, although it's only clear for the first definition. For the second definition, somebody who is confused and scared might lash out and be unblushingly insolent. For the third definition, if you gave assurance to somebody that their actions would have no consequences to them, they might become shameless or unblushingly insolent.
The adjective effronted comes from the French adjective effronté, which also does not appear to have a corresponding verb. And effronté comes from the Latin word effrons, which also gave us effrontery.
Literally, the Latin word effrons means without a forehead. Why that should mean shameless is not entirely clear. Merriam-Webster gives two possible explanations. One of them is:
Some explain that "frons" can also refer to the capacity for blushing, so a person without "frons" would be "unblushing" ...
The word affront comes from the French verb affronter, meaning to confront, to face. This comes from Old French afronter, whose construction would literally mean "to slap on the forehead", but which le trésor de la langue français informatisé says also meant "to shame" and "to confront".
So effronted and affronted in common have the root front, meaning forehead in French. It's possible that the word front was a metonym for blush in the etymology of both of them—so the etymology of effronted would be unblushing, while affront would be to cause to blush (one of its early meanings was shame; the other to slap in the face.).