The Collaborative International Dictionary of English v.0.48:

Ar \Ar\, conj.
   Ere; before. [Obs.] --Chaucer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Ar
    n 1: a colorless and odorless inert gas; one of the six inert
         gases; comprises approximately 1% of the earth's atmosphere
         [syn: argon, Ar, atomic number 18]
    2: a unit of surface area equal to 100 square meters [syn:
       are, ar]
    3: a state in south central United States; one of the
       Confederate states during the American Civil War [syn:
       Arkansas, Land of Opportunity, AR]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

AR
       Administrative Request [message] (LFAP)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

AR
       Aperture Ratio (DVD)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

AR
       Augmented Reality


The Free On-line Dictionary of Computing (30 December 2018):

ar

    The country code for Argentina.

   (1999-01-27)


Hitchcock's Bible Names Dictionary (late 1800's):

Ar, awakening; uncovering