"Sustained" is said of something which continues: "He made a sustained effort." — or sometimes it might mean the same as "nourished" or "fed" (literally or figuratively), and that's where we get the noun "sustenance" meaning food and drink. "Sustainable" in current usage is generally used for farming or industry which won't run out: solar power is "sustainable energy", coal power isn't.

Sustained (adjective)- maintained at length without interruption or weakening e.g. sustained flight Sustainable (adjective)- able to be maintained at a certain rate or level. e.g. "sustainable fusion reactions" or... able to be upheld or defended. e.g. "sustainable definitions of good educational practice" Sources: - Advanced English Dictionary - Google Further Reading: - http://www.vocabulary.com/dictionary/sustained - http://www.vocabulary.com/dictionary/sustainable - http://www.learnersdictionary.com/definition/sustainable - http://sentence.yourdictionary.com/sustained