Main entry: reactive
Definition: participating readily in reactions
Usage: sodium is a reactive metal; free radicals are very reactive
Antonyms: unreactive
Definition: (chemistry) not reacting chemically
Antonyms: unexcited
Definition: not excited
Antonyms: stable
Definition: resistant to change of position or condition
Main entry: reactive, responsive
Definition: reacting to a stimulus
Usage: the skin of old persons is less reactive than that of younger persons
Antonyms: insensitive
Definition: not responsive to physical stimuli
Antonyms: insensitive
Definition: deficient in human sensibility; not mentally or morally sensitive