Definition of "effrontery"

Let not the Englishman in Scotland believe that the undoffed hat, the curt reply, the apparent assumption of equality, all spring from deliberate effrontery, and are wholly beyond the reach of southern influence.

1859, The Christian Remembrancer, volumes 37-38, page 250

All was going as planned until the bag hit a snag and failed to surround the entire nest. This effrontery was too much. The wasps exploded off the nest at me.

2016, Justin O. Schmidt, The Sting of the Wild, Johns Hopkins University Press,, page 92