- Dec 1 Austria has world's 1st Day of Postage Stamp
- Dec 4 1,200 at St Joseph's College (Philadelphia) enroll in anticommunism class
- Dec 5 First commercial hydroponics operation established (Montebello, California)
- Dec 5 National Council of Negro Women forms by Mary McLeod Bethune (NYC)
- Dec 7 CFL Grey Cup, AAA Grounds, Hamilton: Winnipeg Pegs (later Blue Bombers) defeat Hamilton Tigers, 18-12
- Dec 8 The Japanese military police launches a violent suppression of the religious sect Oomoto, beginning with a crackdown on the sect's operational bases of Ayabe and Kameoka in Kyoto Prefecture and the arrest of its leader Onisaburo Deguchi.
- Dec 9 1st Heisman Trophy Award: Jay Berwanger, Chicago (HB)
- Dec 9 Walter Liggett American newspaper editor and muckraker killed in gangland murder.
Neuron Discovery Wins Nobel
Dec 10 James Chadwick is awarded the Nobel Prize for Physics for his discovery of the neutron
Marie Curie Daughter Wins Nobel
Dec 10 Nobel Prize for Chemistry awarded to Irene Joliot-Curie (daughter of Marie Curie) and her husband Frédéric Joliot for the discovery of artificial radioactivity
Foxx to the Red Sox
Dec 10 Philadelphia Athletics sell infielder Jimmie Foxx's contract to Boston Red Sox for $150,000 (about $2.8M in 2020 dollars)
- Dec 10 White Sox sell Al Simmons to the Tigers for $75,000
- Dec 14 Test Cricket debut of "Chuck" Fleetwood-Smith v South Africa, Durban
- Dec 15 In major upset, Dutch grand master Max Euwe becomes World Chess Champion beating Russian Alexander Alekhine (9 wins, 13 draws, 8 losses) in Zandvoort, Netherlands
Detroit Lions' First Title
Dec 15 National Football League Championship, University of Detroit Stadium: Detroit Lions beat New York Giants, 26-7; Lions first title
Douglas DC-3's 1st Flight
Dec 17 1st flight of the Douglas DC-3 (C-47 Skytrain/Dakota) airplane.
Bradman's Sheffield Debut
Dec 18 Don Bradman scores 117 in his debut Sheffield Shield cricket match for South Australia in an innings & 5 run win over his old team, New South Wales
Beneš Succeeds Masaryk
Dec 18 Edvard Beneš becomes President of Czechoslovakia after Tomáš Masaryk retires
- Dec 18 The Lanka Sama Samaja Party is founded in Ceylon
- Dec 22 Yaeko Iwasaki, student of D S Harada Roshi, 1st awakening in Kamakura
- Dec 24 National Council of Negro Women forms
- Dec 28 Pravda publishes a letter by Pavel Postyshev, who revives New Year tree tradition in the Soviet Union
- Dec 28 W P A Federal Art Project Gallery opens in NYC
- Dec 30 Italian bombers destroy Swedish Red Cross unit in Ethiopia
- Dec 31 Charles Darrow patents the board game Monopoly, goes on to be the 1st millionaire game designer
- Dec 31 CPH becomes Dutch Communist Party
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