Definition of side effect noun from the Oxford Advanced American Dictionary

     

    side effect

     noun
    noun
     
    [usually plural]
     
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  1. 1an extra and usually bad effect that a drug has on you, as well as curing illness or pain The drug has few side effects. Side effects include skin rashes and nausea.
  2. 2an unexpected result of a situation or course of action that happens as well as the result you were aiming for Opponents of the policy fear that it could have unfortunate side effects on the economy.
See the Oxford Advanced Learner's Dictionary entry: side effect