Adverse means contrary in purpose or effect, harmful.
Adverse is an adjective.
Synonyms: hostile, opposing, negative, unfriendly, unpropitious, detrimental, antagonistic.
Antonyms: favorable, auspicious.
Note: Don't confuse adverse with averse (uh VURS), which is similar but slightly different in meaning. To be averse to doing something means to be reluctant, opposed, or unwilling to do it. The confirmed bachelor is averse to the idea of marriage.
Don't be discouraged by the adverse criticism of your friends.
Many people are at their best in the face of adversity.
The Air-show program was canceled because of adverse weather.
The patient had an adverse reaction to his medicine; it was detrimental to his health.