| Onslaught | 9 |
| Onslaught of cold weather | 25 |
| Onslaught of crepe orders at a deli? | 36 |
| Onslaughts | 10 |
| Onstage blunder | 15 |
| Onstage boo-boo | 15 |
| Onstage digression | 18 |
| Onstage extra during an aria, for short | 39 |
| Onstage gesture | 15 |
| Onstage ham | 11 |
| Onstage head costume | 20 |
| Onstage phone, e.g. | 19 |
| Onstage strutters | 17 |
| Onstage surprise | 16 |
| Onstage thought balloon | 23 |
| Onstage thought bubble | 22 |
| Onstage, say | 12 |
| OnStar provider | 15 |
| Ont. appliance maker | 20 |
| Ont. channel | 12 |
| Ont. military college | 21 |
| Ont. neighbor | 13 |
| Ont. or Que. | 12 |
| Ont. or Sask. | 13 |
| Ont. police force | 17 |
| Ont. site of a War of 1812 battle | 33 |
| Ont. summer time | 16 |
| Ont. time zone | 14 |
| Ont.'s Capital | 18 |
| Ont.'s neighbor | 19 |
| Ont., for one | 13 |
| Ontarians' national anthem | 30 |
| Ontario community or Polish namesake | 37 |
| Ontario export | 15 |
| Ontario for one | 16 |
| Ontario address | 15 |
| Ontario Ag school | 17 |
| Ontario airbase | 15 |
| Ontario Canadian Forces Base | 28 |
| Ontario cape or former Tory leader Stanfield | 44 |
| Ontario city | 12 |
| Ontario city just west of Buffalo | 33 |
| Ontario community | 17 |
| Ontario community or English namesake | 38 |
| Ontario community or British namesake | 37 |
| Ontario community or the former Taiwan | 38 |
| Ontario county | 14 |
| Ontario feeder | 14 |
| Ontario Forces Base | 19 |
| Ontario Fort | 12 |
| Ontario Freeway, colloquially | 29 |
| Ontario heritage river | 22 |
| Ontario Hockey League team from Erie | 36 |
| Ontario Indian | 14 |
| Ontario is on it | 16 |
| Ontario lake | 12 |
| Ontario metropolis | 18 |
| Ontario native | 14 |
| Ontario natives | 15 |
| Ontario neighbor | 16 |
| Ontario neighbour | 17 |
| Ontario network | 15 |
| Ontario or Michigan | 19 |
| Ontario or Supérieur | 23 |
| Ontario Park, Fort ______ | 26 |
| Ontario politician Bob ___ | 26 |
| Ontario Port | 12 |
| Ontario port opposite Port Huron, Mich. | 39 |
| Ontario Premier | 15 |
| Ontario Premier Bill | 20 |
| Ontario Premier Bob | 19 |
| Ontario Premier Frank | 21 |
| Ontario Premier George | 22 |
| Ontario Premier John | 20 |
| Ontario Premier Leslie | 22 |
| Ontario Premier, formerly | 25 |
| Ontario Premier, once | 21 |
| Ontario raceway | 15 |
| Ontario river | 13 |
| Ontario river to James Bay | 26 |
| Ontario sports org. | 19 |
| Ontario town | 12 |
| Ontario town and French namesake | 33 |
| Ontario town and British namesake | 33 |
| Ontario town or actress Hilton | 30 |
| Ontario town or politician Manning | 34 |
| Ontario town whose sign boasts a giant elephant | 47 |
| Ontario town whose sign boasts a giant mosquito | 47 |
| Ontario town, or a Taurus between a Mustang and a Cougar? | 57 |
| Ontario town, or entertainer Cohen | 34 |
| Ontario tribe | 13 |
| Ontario tribesmen | 17 |
| Ontario TV network | 18 |
| Ontario valley | 14 |
| Ontario village | 15 |
| Ontario village and Turkish namesake | 37 |
| Ontario's 21st premier | 26 |
| Ontario's 23rd Premier | 26 |
| Ontario's bird | 18 |
| Ontario's capital | 21 |