1. responds to a stimulus, situation, or treatment
Usage: third person singular present tense of ‘react’
2. undergoes a chemical change when combined with another substance
Usage: chemistry
3. shows opposition or resistance to something

Examples

• She always reacts quickly to emergencies.
• The crowd reacts with cheers when their team scores.
• Sodium reacts violently with water.
• The metal reacts with oxygen to form rust.
• He reacts badly to criticism.
• The patient reacts well to the new medication.
• The public often reacts negatively to tax increases.