| Opening on an environmentalist's agenda? | 44 |
| Opening of a sewage-filled pool? | 32 |
| Opening of a memorable walrus song | 34 |
| Opening of a letter to a Baltic capital | 39 |
| Opening of a fuel-burning engine | 32 |
| Opening of "A Tale of Two Cities" | 43 |
| Opening number of "Hair" | 34 |
| Opening note to "Carmen"? | 35 |
| Opening note of "Das Rheingold" | 41 |
| Opening night expression (with a hidden veggie) | 47 |
| Opening maneuver to gain advantage | 34 |
| Opening line of a 1966 #1 Beatles hit | 37 |
| Opening line of "Moby-Dork"? | 38 |
| Opening line from someone phoning home | 38 |
| Opening in wastewater management? | 33 |
| Opening in the computer business? | 33 |
| Opening in a popular song for kindergartners | 44 |
| Opening in "Hollywood Squares" | 40 |
| Opening for the wrist or the back? | 34 |
| Opening for peering through a fence | 35 |
| Opening for a young baseball fan | 32 |
| Opening for a letter-shaped bolt | 32 |
| Opening for "state" or "net" | 48 |
| Opening for ''sphere'' | 38 |
| Opening day of the Masters: Abbr. | 33 |
| Opening day of a PGA event, usually | 35 |
| Opening allowing entry of air or fluid | 38 |
| Opening ... machine ... schedule | 32 |
| Opener's second call, in bridge | 35 |
| Opener's next call, in bridge | 33 |
| Opener at an all-Beethoven concert | 34 |
| Opened (or closed), as a shot on a set | 38 |
| Openable with a gentle push, say | 32 |
| Open-mouthed stares from a grouch? | 34 |
| Open-faced sandwich topped with a fancy spread | 46 |
| Open wide and say "baa" | 33 |
| Open the front door for, as a guest | 35 |
| Open someone else's e-mails, maybe | 38 |
| Open mic night participant, e.g. | 32 |
| Open courts used by opera singers? | 34 |
| Open area for Robin Hood's men | 34 |
| Open a prescription bottle, e.g. | 32 |
| OPEC foolishness in a Central Park mix-up? | 42 |
| Opaque-glazed earthenware pieces | 32 |
| Opaque material used in vases, e.g. | 35 |
| Opaque clouds, to meteorologists | 32 |
| Opaque campaign supporters, briefly | 35 |
| Oona in ''Chaplin'' | 35 |
| Oo-la-la leading lady of the 30's | 37 |
| Onto, with ''of'' | 33 |
| Ontario-born hockey legend Bobby | 32 |
| Ontario's St. Lawrence______ | 32 |
| Ontario's second-largest city | 33 |
| Ontario's second most populous city | 39 |
| Ontario's capital, on sports tickers | 40 |
| Ontario's capital, on scoreboards | 37 |
| Ontario's capital, on a scoreboard | 38 |
| Ontario's capital on a sports ticker, | 41 |
| Ontario village and Turkish namesake | 37 |
| Ontario town, or entertainer Cohen | 34 |
| Ontario town whose sign boasts a giant mosquito | 47 |
| Ontario town whose sign boasts a giant elephant | 47 |
| Ontario town or politician Manning | 34 |
| Ontario town and British namesake | 33 |
| Ontario town and French namesake | 33 |
| Ontario port opposite Port Huron, Mich. | 39 |
| Ontario Hockey League team from Erie | 36 |
| Ontario community or the former Taiwan | 38 |
| Ontario community or British namesake | 37 |
| Ontario community or English namesake | 38 |
| Ontario city just west of Buffalo | 33 |
| Ontario cape or former Tory leader Stanfield | 44 |
| Ontario community or Polish namesake | 37 |
| Ont. site of a War of 1812 battle | 33 |
| Onstage extra during an aria, for short | 39 |
| Onslaught of crepe orders at a deli? | 36 |
| Onomatopoeic Sinatra album title | 32 |
| Only X-rated film to win the Best Picture Oscar | 47 |
| Only World Series perfect game pitcher | 38 |
| Only work that Michelangelo signed | 34 |
| Only work of art that Michelangelo signed | 41 |
| Only word heard in a 1958 song of the same name | 47 |
| Only winner of eight consecutive Norris Trophies | 48 |
| Only Wimbledon winner to wear a wig | 35 |
| Only Wimbledon champion to wear a wig | 37 |
| Only when his funny films failed | 32 |
| Only US swimmer to compete in five Olympics | 43 |
| Only US state with two official languages | 41 |
| Only US state with a diamond mine | 33 |
| Only ungulate that mates in the seated position | 47 |
| Only U.S. vice president born in Maryland | 41 |
| Only U.S. state without a rectangular flag | 42 |
| Only U.S. state with a pennant-shaped flag | 42 |
| Only U.S. state whose flag isn't rectangular | 48 |
| Only U.S. president to have three veeps | 39 |
| Only U.S. president born in Hawaii | 34 |
| Only U.N. member whose flag is not rectangular | 46 |
| Only two alphabet letters have them | 35 |
| Only things Noah could afford to take? | 38 |
| Only thing guitarists use w/their feet | 38 |