What is Adverse?

Legal Definition
Adverse or adverse interest, in law, is anything that functions contrary to a party's interest. This word should not be confused with averse.
-- Wikipedia
Legal Definition
Opposed; contrary; In resistance or opposition to a claim, application or proceeding. As to adverse "Claim," "Enjoyment," "Possession," "User," "Verdict," "Witness," see those titles.
-- Black's Law Dictionary