Reactivity

Part of speech: noun

Definitions

1. The characteristic of being able to respond to external changes or stimuli in various contexts, including chemical reactions and physical interactions
2. The property of showing a response to different stimuli or conditions, particularly involving chemical changes and physical reactions
3. The quality of responding to environmental stimuli and changes, which can encompass chemical interactions and physical adjustments

Etymology: Reactivity is a plain English formation: "reactive" with the suffix "-ity" added, meaning "the state or quality of being reactive." The suffix came into English through Old French "-ite" and Latin "-itās," a route that carries it from Latin's abstract-noun endings into English vocabulary. The adjective it rests on is the more interesting part. "Reactive" is built from "re-," meaning "back" or "again," and "act," from Latin "āctus," the past participle of "agere," "to do" or "to drive." Put together, the sense is "acting in return," the core idea that one thing acts back upon another when it is stimulated. Latin "re-" and "āctus" passed through Old French "act" and Middle English "acte" before the English "act" emerged, and "-ive" (ultimately from Latin "-īvus") turned the verb-based root into an adjective. The noun "reactivity" thus describes the capacity for acting back, which is why it now covers both chemical reactions and physical responses to surroundings.

Synonyms: responsiveness, sensitivity, reactiveness

Antonyms: inertness, stability, nonreactivity