responder
UK: /rɪˈspɒndə/ | US: /rɪˈspɑːndər/
n. a person or thing that responds, especially in a specified context (e.g., emergency responder)
n. (Law) a defendant or party answering a legal claim
n. (Technology) a device or system designed to react to specific signals
The word "responder" combines the verb "respond," derived from Latin respondēre ("to answer, promise in return"), with the agentive suffix "-er," indicating "one who does." The Latin root spondēre originally meant "to pledge" (as in solemn promises), evolving into broader meanings of "answer" or "react." The suffix "-er" (from Old English -ere) is productive in forming nouns for roles or tools. Thus, "responder" logically denotes someone or something that answers or reacts—whether a person (e.g., emergency personnel) or a machine (e.g., automated systems).
Paramedics are often the first responders at accident scenes.
The defendant filed a motion as the responder in the lawsuit.
The satellite’s responder transmits data to ground stations.
Community volunteers trained as disaster responders.
The software acts as a responder to user input within milliseconds.