| Operation Overlord site | 23 |
| Operation Overlord time | 23 |
| Operation Overlord vessel, for short | 36 |
| Operation Overlord's time | 29 |
| Operation Overlord, e.g. | 24 |
| Operation Phone Home gp. | 24 |
| Operation Pipe Dreams org. | 26 |
| Operation Red Dawn city | 23 |
| Operation Redwing event, 1956 | 29 |
| Operation reminder | 18 |
| Operation reminders | 19 |
| Operation since August 1990 | 27 |
| Operation Solomon airline | 25 |
| Operation souvenir | 18 |
| Operation specialist | 20 |
| Operation that often precedes an entrapment claim | 49 |
| Operation time | 14 |
| Operation times | 15 |
| Operation Torch setting: Abbr. | 30 |
| Operation Trinity event | 23 |
| Operation Trinity locale | 24 |
| Operation Uphold Democracy site | 31 |
| Operation VIP | 13 |
| Operation __ Freedom (2003-2011 conflict) | 41 |
| Operation ___ Freedom | 21 |
| Operation ___ Freedom (2003) | 28 |
| Operation ____: naval Antarctica project | 40 |
| Operation's start | 21 |
| Operation, e.g. | 15 |
| Operation-launching times | 25 |
| Operational | 11 |
| Operational details, informally | 31 |
| Operational division | 20 |
| Operational headquarters | 24 |
| Operational lines? | 18 |
| Operations are performed in it | 30 |
| Operations center | 17 |
| Operations ctrs. | 16 |
| Operations mgrs. | 16 |
| Operations were once commonly performed in this | 47 |
| Operations, for short | 21 |
| Operative | 9 |
| Operative's employer | 24 |
| Operative's org. | 20 |
| Operative, as a rule | 20 |
| Operative, for short | 20 |
| Operative: Abbr. | 16 |
| Operatives | 10 |
| Operatives' org. | 20 |
| Operatives: Abbr. | 17 |
| Operator | 8 |
| Operator of a metal plant | 25 |
| Operator of drones | 18 |
| Operator of MouthHealthy.org | 28 |
| Operator of the largest brewery facility in the world | 53 |
| Operator of the MilleMiglia program | 35 |
| Operator of the original N.Y.C. subway | 38 |
| Operator order | 14 |
| Operator represented by a downward arrow in symbolic logic | 58 |
| Operator's accessory | 24 |
| Operator's concern: Abbr. | 29 |
| Operator's courteous request | 32 |
| Operator's item | 19 |
| Operator's line | 19 |
| Operator's need | 19 |
| Operator's number? | 22 |
| Operator's place | 20 |
| Operator's post, once | 25 |
| Operator's request | 22 |
| Operator's request? | 23 |
| Operator's wear | 19 |
| Operator, of a sort | 19 |
| Operator, perhaps | 17 |
| Operator: Abbr. | 15 |
| Operators | 9 |
| Operators are involved with them | 32 |
| Operators standing by? | 22 |
| Opercula | 8 |
| Operculum | 9 |
| Operetta character whose son is Nanki-Poo | 41 |
| Operetta composer | 17 |
| Operetta composer Franz | 23 |
| Operetta composer Franz von __ | 30 |
| Operetta division | 17 |
| Operetta man | 12 |
| Operetta part | 13 |
| Operetta princess | 17 |
| Operetta princess and others | 28 |
| Operetta roles | 14 |
| Operetta set in Titipu | 22 |
| Operetta team | 13 |
| Operetta with Nanki-Poo and Yum-Yum, with "The" | 57 |
| Operettist Franz | 16 |
| Opeth "Watershed" opener | 34 |
| Ophelia and Hamlet, e.g. | 24 |
| Ophelia or Claudius, e.g. | 25 |
| Ophelia or Horatio | 18 |
| Ophelia or Laertes, e.g. | 24 |
| Ophelia's avenger | 21 |
| Ophelia's brother | 21 |