The problem with this term in English is that it can mean 'going on and on' and so plastic or plutonium isotopes may go on and on but this not necessarily mean sustainable as it is usually used. In Ireland there is a lot of talk about 'sustainable' jobs and this usually refers to jobs that will somehow magically survive the next financial meltdown and again doesn't refer to true sustainability.
If we look at other languages the root of the term used for sustainability is often different. So in Gaelic the term is 'inbhuaindearacht' and the root of that is more to do with stewardship or guardianship which is very different to 'going on and on'. In Swedish the term is 'halbaret' and the root of this refers to balance. Many languages use the term sustainability and I believe we need to be careful how we use the term.