The Collaborative International Dictionary of English v.0.48:

Supportable \Sup*port"a*ble\, a. [Cf. F. supportable.]
   Capable of being supported, maintained, or endured;
   endurable. -- Sup*port"a*ble*ness, n. -- Sup*port"a*bly,
   adv.
   [1913 Webster]