ETYMOLOGY
from Latin adversarius (opposed, hostile, adverse, harmful, injurious) + -ous
EXAMPLE
“…This resisting and aduersarious Empire, while it fought against Christ it serued Christ, while it killed his Church it increased his Church, and while it fought against Religion, it became a meanes to spread and inlarge it…”
From: Diseases of the Time Attended by their Remedies
By Francis Rous, 1622
Lexicophilia 