> An elastic band is extensible, ie: it can be stretched, whereas my lunch hour is extendable, ie: it can be added to, but an hour is an hour and cannot be stretched.

That makes plenty of sense, but it seems some think that exactly the opposite should be the case. I think if I have to settle one way or the other I'll opt for your definitions, dxb.

> There is also extensile which seems to mean the same as extensible.

Don't go extensiling things.