Historical clue formulations

• Greek letter that symbolizes an angle — 2026-08-17
• Angle variable, in math — 2026-05-01
• Angle symbol, in geometry — 2026-01-13
• Variable representing an angle, in math — 2025-03-01
• Letter before iota — 2024-12-22
• Angle symbol, in trigonometry — 2023-10-12
• Symbol for an angle in math — 2023-02-23
• Letter before iota — 2022-01-10
• Letter in the Greek spelling of Athens — 2022-01-07
• Sorority letter — 2021-11-21
• Certain sorority member — 2021-08-07
• Thucydides had one — 2020-05-24
• Letter before iota — 2020-01-20
• Angle symbol in geometry — 2019-09-29
• Letter found between two vowels in the alphabet — 2019-07-12
• Iota preceder — 2018-01-30
• Symbol for a plane angle, in geometry — 2017-09-22
• Symbol in trigonometry — 2017-05-21
• Trig angle symbol — 2016-07-24
• Letter before 23-Across — 2015-11-03
• First letter in "Thanatos" — 2015-09-17
• See 22-Across — 2015-09-16
• Letter accompanying sin? — 2015-07-03
• Certain sorority member — 2015-01-24
• Certain sorority woman — 2014-03-25
• Greek letter traditionally associated with Earth Day — 2013-11-05
• Certain sorority woman — 2013-01-20
• Letter before iota — 2012-08-13
• Letter after eta — 2011-10-10
• Angle symbol, in trigonometry — 2011-09-28
• Angle symbol, in trigonometry — 2010-12-15
• Letter before iota — 2008-10-14
• Letter between eta and iota — 2008-07-22
• Sorority letter — 2008-04-10
• Fraternity letter — 2008-03-06
• Sorority letter — 2006-05-03
• Oval letter with a line through the middle — 2006-02-21
• Certain sorority member — 2004-11-21
• Certain sorority woman — 2003-01-01
• Angle measurement symbol — 2002-10-25
• Letter before iota — 2002-05-06
• Letter before 29-Down — 2002-03-04
• Sorority letter — 2001-07-02
• Temperature symbol — 2000-12-03
• Fraternity letter — 1999-11-25
• Iota preceder — 1999-10-25
• Kind of radiation, in science fiction — 1999-07-04
• Angle symbol — 1998-10-27
• Eta follower — 1997-11-24
• It's between eta and iota — 1997-01-29