reading, 'riting, and 'rithmetic, regarded as the fundamentals of education.
the fundamentals, basic knowledge, or skills of any system or field: the three R's of good government.
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British Dictionary definitions for three Rs
the three Rs the three skills regarded as the fundamentals of education; reading, writing, and arithmetic
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
Other Idioms and Phrases with three R's
The fundamentals of education, as in It's a terrible school; the children are not even taught the three R's. It is widely believed that Sir William Curtis, an alderman who became Lord Mayor of London, once presented a toast to the three R's—reading, riting, and rithmetic—thereby betraying his illiteracy. In any event, the term was picked up by others and so used from the early 1800s on.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.