A Catalyst

1. (chemistry) A substance that increases the rate of a chemical reaction without being consumed in the process.
2. Someone or something that encourages progress or change.
3. (literature) An inciting incident that sets the successive conflict into motion.
4. (automotive) A catalytic converter.

Synonyms

• (Someone or something that encourages progress or change): stimulus, straw that stirs the drink

Antonyms

• (something that encourages change): inhibitor
• (something that enhances or accelerates): dampener