| 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 |
| An oz. has six | 14 |
| An RN gives it | 14 |
| An S.S.R. | 9 |
| An S.S.R. language | 18 |
| An SASE is one | 14 |
| An SASE may accompany one | 25 |
| An SI unit | 10 |
| An SST | 6 |
| An SUV's is relatively low | 30 |
| An SUV's may be 12 | 22 |
| An udder thing | 14 |
| An ump is paid to make it | 25 |
| An umpire is behind it | 22 |
| An umpire makes it | 18 |
| An unbelievable tale | 20 |
| An unbreakable substance | 24 |
| An uncle of Joseph | 18 |
| An uncle of Mohammed | 20 |
| An uncle of Saul | 16 |
| An uncultivated person | 22 |
| An undesirable thing | 20 |
| An undesirable thing to be in | 29 |
| An unenjoyable experience | 25 |
| An unfinished figure 8 | 22 |
| An unfinished figure eight? | 27 |
| An unforgettable meal | 21 |
| An ungulate | 11 |
| An unknown quantity | 19 |
| An unlikely beginning | 21 |
| An unmannerly spectre | 22 |
| An unmentionable | 16 |
| An unsaturated hydrocarbon | 26 |
| An unsolicited script, e.g. | 27 |
| An unspecified amount | 21 |
| An unspecified number | 21 |
| An unthinking way | 17 |
| An Untouchable | 14 |
| An untouchable one | 18 |
| An unused item may be placed in it | 34 |
| An unwanted impression | 22 |
| An unwanted lasting impression | 30 |
| An unwelcome guest, to Galba | 28 |