adverse

Steer clear of anything adverse. If it’s adverse, it’s working against you — like adverse weather conditions or the adverse effects of eating too much sugar.

Coming from the Latin adversus meaning “turned against,” adverse is an adjective describing a factor that seems to work against or actively harm something. Think of the related word, adversary, which means “enemy or opponent,” so that if something is adverse, it acts as if it were the enemy. If you have an adverse reaction to an antibiotic, your doctor will need to prescribe a new medication.