| 100% | INITIATOR | 9 | Substance that starts a chain reaction |
| 61% | CATALYST | 8 | Substance that accelerates a chemical reaction |
| 61% | CATALYST | 8 | Substance that boosts a chemical reaction |
| 61% | CATALYST | 8 | Substance that precipitates a chemical reaction |
| 59% | CATALYST | 8 | Substance that speeds up a reaction |
| 58% | CATALYST | 8 | Trigger that starts a reaction |
| 55% | INHIBITOR | 9 | Substance that slows down a chemical reaction |
| 52% | CATALYST | 8 | A substance that speeds up a chemical reaction |
| 45% | CRITICALMASS | 12 | What a chain reaction requires |
| 45% | DOMINO | 6 | Tile in a chain reaction |
| 45% | WWW | 3 | Letters that start a URL |
| 45% | PREAMBLE | 8 | Introductory statement that starts a book |
| 45% | KICKOFF | 7 | Play that starts a football game |
| 45% | ANTE | 4 | Poker chip that starts a pot |
| 45% | CAROL | 5 | Dickens' novel that starts A Christmas |
| 45% | ABC | 3 | Letters that start a kindergarten tune |
| 45% | THEFEMININEMYSTIQUE | 19 | 1963 book that started a movement |
| 44% | LENIN | 5 | Name that starts a well-known "ism" |
| 44% | DEAR | 4 | "___ Diary," words that start a diary entry |
| 44% | YOUREIT | 7 | Words that start a game of tag |
| 44% | FIREUP | 6 | To provoke, start a reaction |
| 43% | BRYN | 4 | Welsh word that starts a noted college name |
| 43% | HELLO | 5 | Word of greeting that starts a phone conversation |
| 43% | AREA | 4 | ___ code (three digits that start a phone number) |
| 43% | PSI | 3 | Three letters that start a Beatles song title |
| 43% | SIXTEEN | 7 | Number of pawns that start a chess game |
| 43% | ENZYME | 6 | Substance that speeds up biochemical reactions |
| 43% | ENZYME | 6 | Substance that sets off chemical reactions |
| 43% | SPIT | 4 | Substance that flattens a kiss curl |
| 43% | ACTIVATE | 8 | Set in motion, start a reaction |