The Collaborative International Dictionary of English v.0.48:

Importable \Im*port"a*ble\, a. [L. importabilis; pref. im- not +
   portabilis bearable: cf. OF. importable. See Portable.]
   Not to be endured; insupportable; intolerable. [Obs.]
   --Chaucer. -- Im*port"a*ble*ness, n. [Obs.]
   [1913 Webster]