Historical clue formulations

• Lower — 2014-07-18
• Cheapen — 2009-10-15
• Lower the value of, as currency — 2008-09-08
• Adulterate — 2002-05-15
• Knock down — 2002-04-02
• Pollute — 2000-10-09
• Cheapen — 1999-11-21
• Adulterate — 1997-01-24
• Lower — 1994-07-10
• Pollute — 1994-03-20
• Adulterate — 1994-02-17