| Ontario Park, Fort ______ | 26 |
| Ontario or Supérieur | 23 |
| Ontario heritage river | 22 |
| Ontario Freeway, colloquially | 29 |
| Ontario Canadian Forces Base | 28 |
| Onstage thought bubble | 22 |
| Onstage thought balloon | 23 |
| Onslaught of cold weather | 25 |
| Onset of enthusiasm, perhaps | 28 |
| Onomatopoetic water sound | 25 |
| Onomatopoeically named legume | 29 |
| Onomasticon's contents | 26 |
| Onomastician's study | 24 |
| Only women understand one | 25 |
| Only woman to outwit Holmes | 27 |
| Only with for the money, say | 28 |
| Only what a person can take? | 28 |
| Only Welsh-born Batman | 22 |
| Only wants for sex, say | 23 |
| Only Veep from Maryland | 23 |
| Only U.S. pres. to resign | 25 |
| Only three-letter element | 25 |
| Only this, and nothing else | 27 |
| Only tavern in Springfield | 26 |
| Only state with homonyms | 24 |
| Only South Dakota-born VP | 25 |
| Only son of Czar Nicholas II | 28 |
| Only remaining heater? | 22 |
| Only president born in Hawaii | 29 |
| Only pres. born in Missouri | 27 |
| Only pope from England | 22 |
| Only part of Egypt in Asia | 26 |
| Only Pacific island monarchy | 28 |
| Only openings for air? | 22 |
| Only one-syllable state name | 28 |
| Only one-syllable state | 23 |
| Only occupant of Vostok I | 25 |
| Only monosyllabic state | 23 |
| Only making the grade? | 22 |
| Only just broke the tape | 24 |
| Only inanimate zodiac sign | 26 |
| Only four-letter Great Lake | 27 |
| Only female attorney general | 28 |
| Only even prime number | 22 |
| Only daughter of Elizabeth II | 29 |
| Only creature that blushes | 26 |
| Only Canadian MLB team | 22 |
| Only beardless Disney dwarf | 27 |
| Only ape to circle the earth | 28 |
| Only Adam and Eve lacked them | 29 |
| Only a stone's throw away | 29 |
| Only a drug of forgetfulness? | 29 |
| Only a bit in debt, perhaps | 27 |
| Online-only publication | 23 |
| Online voice calling service | 28 |
| Online video equipment | 22 |
| Online user's self-image | 28 |
| Online used vehicle dealer | 26 |
| Online university suffix | 24 |
| Online university staff? | 24 |
| Online university extension | 27 |
| Online travel reservation | 25 |
| Online tracking devices | 23 |
| Online technical news source | 28 |
| Online tech-news source | 23 |
| Online tech news source | 23 |
| Online tech news resource | 25 |
| Online suffix with Net | 22 |
| Online subscription inits. | 26 |
| Online stores, collectively | 27 |
| Online source for TV shows | 26 |
| Online software come-on | 23 |
| Online social appointment | 25 |
| Online sidebar headings | 23 |
| Online shopping outlay | 22 |
| Online shopping center | 22 |
| Online shoppers might use it | 28 |
| Online shopper's basket | 27 |
| Online seller's site | 24 |
| Online revenue sources | 22 |
| Online return returner | 22 |
| Online retailer, perhaps | 24 |
| Online registration creations | 29 |
| Online reference source | 23 |
| Online recruiting site | 22 |
| Online realm since 2006 | 23 |
| Online reading, briefly | 23 |
| Online reading material | 23 |
| Online read, for short | 22 |
| Online queries, briefly | 23 |
| Online qualifier, initially | 27 |
| Online purchase option | 22 |
| Online purchase facilitator | 27 |
| Online publications, briefly | 28 |
| Online publication, for short | 29 |
| Online profile category | 23 |
| Online prefix with -pedia | 25 |
| Online political magazine | 25 |
| Online place for rants | 22 |
| Online periodical, for short | 28 |