Defining marriage for dictionary makers is easy. Its whatever THE STATE SAYS IT IS, since you need the state sanction for marriage. In most of the world, its between a man and a woman, in some parts it doesn't matter what gender; and in some parts of the world, marriage is between a man, a woman, the man's parents, the woman's parents, and a corrupt Indian priest you have to pay off with a few ruples.

Defining sexual acts is a bit more difficult. But don't blame the prudes alone for our imability to define sexual terms. Blame Bill Clinton.

Writing the rest of the dictionary is pretty annoying as well when you consider that you actually need words in order to define other words. So, do you make the dictonary completely self-contained (which would defeat its purpose); or do you acknnoledge that everybody who speaks the language knows what all the preposiitons, articles, helping verbs, and other common words mean. I mean we all agree on the definition of "definition", "dictionary", "the" and "is**".

** Well, unless you're Bill Clinton.