| An old couple fell in it | 24 |
| An old flame's pastime? | 27 |
| An old glory | 12 |
| An Old Glory color | 18 |
| An old master | 13 |
| An old one may need a key | 25 |
| An old ruse: Colloq. | 20 |
| An old secretary might sit in one | 33 |
| An old story | 12 |
| An old story from Paul? | 23 |
| An old syllable meaning "before" | 42 |
| An old tire, perhaps | 20 |
| An old tongue | 13 |
| An old Warner Bros. production? | 31 |
| An old-timer | 12 |
| An older brother of Seth | 24 |
| An older one may be beaten | 26 |
| An oleoresin | 12 |
| An olive is one | 15 |
| An Olivier co-star: 1939 | 24 |
| An Olympian | 11 |
| An Olympian may thrust it | 25 |
| An Olympic medal | 16 |
| An Olympic ring | 15 |
| An Olympic swimmer may have a long one | 38 |
| An Olympic swimmer needs a big one | 34 |
| An Olympic swimming champ: 1932 | 31 |
| An Olympic team | 15 |
| An Olympic twin | 15 |
| An Olympics site: 1988 | 22 |
| An Olympics star in 1936 | 24 |
| An omega stands for it | 22 |
| An omen might do it well | 24 |
| An Onassis | 10 |
| An Onassis nickname | 19 |
| An Onassis, for short | 21 |
| An op-ed has one | 16 |
| An OPEC land | 12 |
| An opening line | 15 |
| An operatic plant? | 18 |
| An operative | 12 |
| An operator may call on one | 27 |
| An operator may help place one | 30 |
| An ophidian | 11 |
| An opponent of | 14 |
| An opposite of down | 19 |
| An opposite of to | 17 |
| An orange, minus the juice | 26 |
| An orangutan | 12 |
| An orator's may rise and fall | 33 |
| An orb or god | 13 |
| An orb-weaving spider with black markings resembling a mustache was named after this musician | 93 |
| An orchestra tunes to one | 25 |
| An order of angels | 18 |
| An order of herbaceous plants | 29 |
| An order of Hindu monks | 23 |
| An order of rank | 16 |
| An order of the court | 21 |
| An order to a helmsman | 22 |
| An orderly grouping | 19 |
| An ore of uranium | 17 |
| An Oreo has three | 17 |
| An org. under F.D.R. | 20 |
| An organ stop | 13 |
| An organic compound | 19 |
| An organized society | 20 |
| An original Baby Bell | 21 |
| An original eurozone member | 27 |
| An original member of the Star Alliance | 39 |
| An original Mouseketeer | 23 |
| An original sinner | 18 |
| An original Star Alliance airline | 33 |
| An original tribe of Israel | 27 |
| An orthodontist ___ | 19 |
| An Oscar | 8 |
| An Oscar is mostly this | 23 |
| An Oscar role for Hanks | 23 |
| An Oscar winner in "On Golden Pond" | 45 |
| An Oscar winner in 1960 | 23 |
| An Oscar winner in 1977 | 23 |
| An Oscar winner in 1986 | 23 |
| An Oscar winner: 1931-32 | 24 |
| An Oscar winner: 1942 | 21 |
| An Oscar winner: 1990 | 21 |
| An Oscar-winning screenwriter of "Casablanca" | 55 |
| An Osmond | 9 |
| An Osmond brother | 17 |
| An ostrich's weighs about three pounds | 42 |
| An otherwise well-behaved liar? | 31 |
| An Ott | 6 |
| An ounce of this is worth the alternative | 41 |
| An outbacker | 12 |
| An outfield field | 17 |
| An outfielder may call it | 25 |
| An outside limit | 16 |
| An overabundance | 16 |
| An overdose of | 14 |
| An overhand smash might hit it | 30 |
| An overworked horse | 19 |
| An Oxford college | 17 |