Ontology, taxonomy and etymology

In addition to having a lot of O's, these words have something else in common: their meanings have to be looked up every time you encounter them. You come across them in the course of your reading, a dim light goes off somewhere in the recesses of your brain, but it's not bright enough to avoid a lookup, and off you go to reference.com.

I used to consider semantics in the same category, but nailed it firmly by taking recourse to XML: if an XML document is well-formed, it's syntactically correct, while it has to be valid (i.e. satisfy a schema/DTD) to be semantically correct. I guess there is something to the rumour that XML can solve world hunger, if only we would let it.