The Collaborative International Dictionary of English v.0.48:

Arable \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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Arable \Ar"a*ble\, n.
   Arable land; plow land.
   [1913 Webster]

WordNet (r) 3.0 (2006):

arable
    adj 1: (of farmland) capable of being farmed productively [syn:
           arable, cultivable, cultivatable, tillable]