-able suff. 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."
Collaborative International Dictionary of English 0.48