Hips, haws and drupes: when is a nut not a nut?

It's the season of mists and mellow fruitfulness - not to mention chestnuts roasting on an open fire. But many of the "nuts" we eat are nothing of the sort

Any self-respecting pub quiz bore will tell you a peanut is a legume, a relative of the pea. If they are on top of their game, they will take pride in their certain knowledge that pineapples are, in fact, coalesced berries; there'll be discussion of bananas no doubt. But, what of hips and haws? What about drupes? And, perhaps of more seasonal importance: what makes a "true nut", in the strictest biological definition?