I've said this often in the past, but I seem to repeat it all the time to people who think that "green growth" is an oxymoron or that we don't need the environment (or economy) to have a good life.
Economic sustainability implies that business can carry on indefinitely, because goods and services are being produced and traded in a way that creates value for vendors, producers and consumers.
Environmental sustainability implies that an activity can continue indefinitely, because human activities do not disrupt natural cycles that deliver environmental services to us, directly (clean water) or indirectly (healthy ecosystems).
See how they fit together? See how "unsustainable" practices in either knock the other off balance?
Now go be sustainable!