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hump day

noun
  1. informal the middle day of the working week, usually Wednesday

Word Origin for hump day

C20: see hump (sense 5)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012