ArThe symbol for argon.ARabbr.1. accounts receivable2. Arkansas3. army regulationar 1 (är)n. Variant of are2.ar 2 (är)n. The letter r.[Middle English arre, from Late Latin er.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.ar the internet domain name for (Computer Science) Argentina Ar the chemical symbol for (Elements & Compounds) argon AR abbreviation for 1. (Placename) Arkansas 2. (Government, Politics & Diplomacy) Autonomous Region 3. (Accounting & Book-keeping) Also: A/R (in the US and Canada) accounts receivable Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ar- var. of ad- before r: arrear. -ar1 , var. of -al1, joined to words in which an l precedes the suffix: circular; lunar; singular. [