| 2026-07-16 | Heavens |
| 2026-07-08 | Heavens |
| 2025-12-21 | Air |
| 2025-11-10 | Old-time anesthetic |
| 2025-10-28 | Thin air |
| 2025-10-24 | Number discovered in the 1500s |
| 2025-09-07 | Anesthetic first used on a patient in 1842 |
| 2025-07-07 | Heavens |
| 2024-12-25 | Upper atmosphere |
| 2024-02-23 | Early number? |
| 2023-03-31 | Heavens |
| 2022-12-15 | Anesthetic since the 1840s |
| 2022-04-01 | Upper atmosphere |
| 2022-03-17 | Air up there |
| 2022-02-27 | Onetime dentist's supply |
| 2021-12-19 | It'll knock you out |
| 2021-12-18 | Heavens |
| 2021-04-17 | Clear sky |
| 2021-04-08 | Upper atmosphere, with "the" |
| 2021-03-26 | Fifth element, to Aristotle |
| 2021-01-13 | Thin air |
| 2020-08-30 | Anesthetic of old |
| 2020-08-11 | Old anesthetic |
| 2020-04-22 | It's a knockout |
| 2020-03-06 | Old knockout? |
| 2019-11-11 | Old anesthetic |
| 2019-10-14 | Old anesthetic |
| 2019-07-14 | Old dentist's supply |
| 2019-06-30 | What radio signals travel through, with "the" |
| 2018-08-05 | Antiquated anesthetic |
| 2018-07-04 | Bygone anesthetic |
| 2018-04-08 | Anesthetic of old |
| 2017-09-18 | Heavens, poetically |
| 2017-06-11 | It'll knock you out |
| 2017-05-23 | Early anesthetic |
| 2017-02-16 | It will put you to sleep |
| 2017-01-18 | Anesthetic of old |
| 2016-11-08 | Surgeon's supply in the old days |
| 2016-06-30 | Thin air |
| 2016-04-17 | Upper reaches |
| 2016-03-02 | Early anesthetic |
| 2016-02-24 | Upper reaches of space |
| 2016-01-13 | Old anesthetic |
| 2015-09-18 | It's a knockout |
| 2015-04-14 | Lead-in to net |
| 2014-07-13 | Clear sky |
| 2014-06-29 | C4H10O |
| 2014-05-01 | Heavens |
| 2014-03-28 | Upper regions of space |
| 2014-01-05 | It's a knockout |
| 2013-09-11 | Dr. Larch's drug in "The Cider House Rules" |
| 2013-01-19 | Dioxane, e.g. |
| 2012-10-18 | Knockout number? |
| 2012-07-29 | Aristotle's "fifth element" |
| 2012-02-25 | Fifth element, per Aristotle |
| 2012-01-02 | Air up there |
| 2011-10-31 | Old-time anesthetic |
| 2011-10-24 | Once-popular anesthetic |
| 2011-07-19 | Old anesthetic |
| 2010-01-11 | Bygone anesthetic |
| 2009-01-09 | Clear sky |
| 2008-09-25 | One on it may be out of it |
| 2008-08-11 | Onetime dental anesthetic |
| 2007-04-29 | Compound number? |
| 2007-01-03 | Dimethyl ___ (aerosol propellant) |
| 2006-12-28 | Upper sky |
| 2005-12-19 | Upper atmosphere |
| 2005-05-30 | Potent anesthetic |
| 2005-03-06 | It can knock people out |
| 2005-03-01 | Old anesthetic |
| 2004-11-09 | It'll knock you out |
| 2004-06-23 | It'll knock you out |
| 2004-04-19 | Old-fashioned anesthetic |
| 2004-02-01 | It's a knockout |
| 2003-06-03 | Early anesthetic |
| 2002-07-07 | Old hospital administration |
| 2002-06-20 | Composition of outer space, in old belief |
| 2002-06-17 | It'll knock you out |
| 2002-02-11 | Obsolete anesthetic |
| 2002-01-07 | It'll knock you out |
| 2001-12-27 | It puts people out |
| 2001-12-05 | Upper region of space |
| 2001-11-19 | Bygone anesthetic |
| 2001-09-12 | Early anesthetic |
| 2001-08-17 | Preoperative delivery of old |
| 2001-04-01 | Part of the gasoline additive M.T.B.E. |
| 2001-02-12 | Cousin of chloroform |
| 2000-07-15 | Air beyond the clouds |
| 2000-07-02 | It's a knockout |
| 1999-09-05 | Preoperative delivery, once |
| 1999-06-21 | Old anesthetic |
| 1999-02-27 | What a knockout! |
| 1998-10-22 | Pre-op inhalant, once |
| 1998-03-12 | Pre-Novocain stuff |
| 1998-02-07 | Common solvent |
| 1997-08-20 | Early anesthetic |
| 1996-11-19 | Old-time anesthetic |
| 1995-07-16 | Space, to poets |
| 1995-04-05 | Flammable anesthetic |
| 1995-01-28 | Preparation for drilling? |
| 1995-01-25 | Clear sky |
| 1995-01-05 | Anesthetic |
| 1994-12-24 | Wild blue yonder |
| 1994-10-12 | Dentist's gas |
| 1994-07-13 | Old anesthetic |
| 1994-06-18 | Clear sky |
| 1994-04-17 | Dentist's supply, once |
| 1994-03-02 | Chloroform kin |
| 1994-02-14 | Upper regions of space |
| 1994-02-08 | Anesthetic gas |