From the Oxford Dictionary
An action or remark that causes outrage or offence.
Effront is not in any of the major modern dictionaries including the Oxford dictionary, however it is cited in wiktionary from the 1913 Webster's dictionary as
To give assurance to.
Effrontery is listed in the modern day Oxford Dictionary as well as other dictionaries
Insolent or impertinent behaviour.
I came across this word as a crossword answer for the clue Brass Neck which made me assume that Effrontery was the action of Effronting or performing an Effront. However it does not seem to be the case and the historic definition of Effront appears to be something else entirely. I would not have been surprised to have seen the definition of Affront appearing as the definition for Effront because they seem connected.
Are these words all related somehow? I could not find much about the etymology.
Thanks for the link to etymonline I haven't come across that before. It explains that there was an Effront but it disappeared. It says to compare Effrontery with Affront but it offers no explanation of how it came to be. Looking up Affront on there shows Related: Affronted; affronting. but no Affrontery and the meaning is worded differently perhaps they are considered interchangable.
I would like to know how we ended up with some words beginning with A and some beginning with E and why there are certain variations that do not exist in each set. Seems strange.