The Collaborative International Dictionary of English v.0.48:

Workable \Work"a*ble\, a.
   Capable of being worked, or worth working; as, a workable
   mine; workable clay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

workable
    adj 1: capable of being done with means at hand and
           circumstances as they are [syn: feasible, executable,
           practicable, viable, workable]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "workable":
   achievable, actable, answerable, applicable, ascertainable,
   attainable, banausic, capable of solution, compassable,
   decipherable, decodable, determinable, doable, effective,
   effectual, efficient, explainable, explicable, exploitable,
   feasible, manageable, maneuverable, manipulatable, negotiable,
   open to solution, operable, operatable, overcomable, performable,
   practicable, practical, pragmatic, realizable, resolvable, soluble,
   solvable, superable, surmountable, usable, viable