ETYMOLOGY
either from affront (n.) or affront (vb.) + -ous,
perhaps after Middle French affronteur (opposing, attacking)
EXAMPLE
“…for those Counsels are sufficient honourable, which render securitie vnto doubtfull affaires. And on the contrary, those are most affrontous, & miserable; when being enterprised with temeritie, onely to shew a vaine presumption, and rigorous boldnesse of minde, they are wont to disturbe the good courses of the honorable enterprises, and of the victories whereof great hope is to be had…”
From: The Theorike and Practike of Moderne Warres
By Robert Barret, 1598
Lexicophilia 