1 the unpleasant effect that a drug may have in addition to its useful effects 副作用: Side effects of the drug include nausea and dizziness. 这种药物的副作用包括恶心和头晕。

2 an unexpected effect of sth that happens in addition to the intended effect 意外后果: One of the side effects when the chemical factory closed was that fish returned to the river. 化工厂关闭以后，鱼类返回河里，算是出乎意料的结果之一。 ☞Look at after-effect and effect. 参看after-effect及effect。