ARABLE is a 6 letter word that starts with A.

1. \Ar"a*ble\, a. [F. arable, L. arabilis, fr. arare to
   plow, akin to Gr. ?, E. ear, to plow. See {Earable}.]
   Fit for plowing or tillage; -- hence, often applied to land
   which has been plowed or tilled.
   

2. \Ar"a*ble\, n.
   Arable land; plow land.