Reactor (noun)

1. A device or vessel in which a reaction takes place, especially a nuclear reaction.
2. A person who reacts strongly to a particular situation or stimulus.

Origin:

Late 19th century: from french réacteur, from réagir "react".

Examples:

1. The nuclear reactor produced energy for the city.
2. The reactor was shut down for safety reasons.
3. The chemist designed a new type of reactor for the experiment.
4. The audience member was a passionate reactor to the speaker's words.
5. The patient was a reactor to the medication and showed improvement.