A unit of quantity equal to 2. The word is from the Latin paria, meaning "equals." Originally a pair was simply a group of similar objects, number unspecified. Eventually this meaning was specialized to refer to a group of two
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}