The Collaborative International Dictionary of English v.0.48:

Are \Are\, n. [F., fr. L. area. See Area.] (Metric system)
   The unit of superficial measure, being a square of which each
   side is ten meters in length; 100 square meters, or about
   119.6 square yards.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Are \Are\ [AS. (Northumbrian) aron, akin to the 1st pers. pl.
   forms, Icel. erum, Goth. sijum, L. sumus, Gr. ?, Skr. smas;
   all from a root as. ? See Am and Is, and cf. Be.]
   The present indicative plural of the substantive verb to be;
   but etymologically a different word from be, or was. Am, art,
   are, and is, all come from the root as.
   [1913 Webster]

WordNet (r) 3.0 (2006):

are
    n 1: a unit of surface area equal to 100 square meters [syn:
         are, ar]

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

ARE
       All Routes Explorer (ATM)


Bouvier's Law Dictionary, Revised 6th Ed (1856):

ARE. A French measure of surface. This is a square, the sides of which are
of the length of ten metres. The are is equal to 1076.441 square feet. Vide
Measure.