effrontery: [18] The notion of ‘audacity’ or ‘impudence’ is often expressed in terms of ‘exposing or pushing forward the face’: a ‘barefaced lie’ or ‘putting on a bold front’, for instance. And effrontery is no exception. It comes ultimately from late Latin effrōns ‘barefaced, shameless’, a compound adjective formed from the prefix ex- ‘out of’ and frōns ‘forehead’ (source of English front).
This seems subsequently to have been reformulated along the lines of its original components, giving Vulgar Latin *exfrontātus, source of Old French esfronte. This in turn developed to French effronté, whose derived noun effronterie was acquired by English as effrontery. => front
