1A person who replies to something, especially one supplying information for a questionnaire or responding to an advertisement.
- ‘the vast majority of responders indicated that the advertisement was believable’
2A person who reacts quickly or positively to a stimulus or treatment.
- ‘the change had already occurred in placebo responders at week one’
3A person trained to respond to and deal with emergencies.
- ‘these factors facilitated quick pathways for disaster responders’