Source : Webster's Revised Unabridged Dictionary (1913)

-able \-a*ble\ (-[.a]*b'l). [F. -able, L. -abilis.]
   An adjective suffix now usually in a passive sense; able to
   be; fit to be; expressing capacity or worthiness in a passive
   sense; as, movable, able to be moved; amendable, able to be
   amended; blamable, fit to be blamed; salable.

   Note: The form {-ible} is used in the same sense.

   Note: It is difficult to say when we are not to use -able
         instead of -ible. ``Yet a rule may be laid down as to
         when we are to use it. To all verbs, then, from the
         Anglo-Saxon, to all based on the uncorrupted
         infinitival stems of Latin verbs of the first
         conjugation, and to all substantives, whencesoever
         sprung, we annex -able only.'' --Fitzed. Hall.