Historical clue formulations

• Hardens (to) — 2023-09-19
• Hardens — 2023-01-14
• Toughens — 2020-07-03
• Gets used (to) — 2020-04-05
• Habituates — 2019-10-23
• Hardens — 2013-02-24
• Accustoms — 2010-08-01
• Habituates — 2009-07-23
• Hardens — 2009-03-09
• Hardens — 2006-11-19
• Toughens — 2006-06-25
• Gets used (to) — 1997-08-26
• Habituates — 1997-08-17
• Habituates — 1997-01-02