ARE is a 3 letter word that starts with A.

1. \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.
   
   

2. \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.