sustainable

from WordNet (r) 3.0 (2006)

sustainable
    adj 1: capable of being sustained

from The Collaborative International Dictionary of English v.0.48

Sustainable \Sus*tain"a*ble\, a. [Cf. F. soutenable, OF.
   soustenable.]
   Capable of being sustained or maintained; as, the action is
   not sustainable.
   [1913 Webster]