Monday hammer

Monday hammer
 n.— «Workers at construction sites use a very heavy hammer to break rocks and concrete. They call it a “Monday hammer.” Why “Monday hammer?” Because, they say, on Mondays they come to work fresh and strong, having rested over the weekend and therefore are able to wield this heavy hammer.» —“Daily Devotions: Monday Hammer” Lutheran Hour Ministries (St. Louis, Mo.) Jan. 27, 2005. (source: Double-Tongued Dictionary)