noun

• 1A person who replies to something, especially one supplying information for a questionnaire or responding to an advertisement.

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  • ‘the vast majority of responders indicated that the advertisement was believable’

• 2A person who reacts quickly or positively to a stimulus or treatment.

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  • ‘the change had already occurred in placebo responders at week one’

• 3A person trained to respond to and deal with emergencies.

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  • ‘these factors facilitated quick pathways for disaster responders’