Historical clue formulations

• Tune — 2020-01-20
• Tune — 2015-05-11
• Principal part — 2014-08-01
• Tune — 2012-12-17
• Series of notes — 2010-03-07
• It may have a hook — 1999-12-24
• Strain — 1999-06-05
• It's hummed — 1993-12-27