Ridiculous

Today in the comments section of a website I noticed the misspelling "obsurd". (I'm not telling you which website and I'm not singling out the comment's author for ridicule, either. It's just a mistake, that's all.) It is, of course, "absurd", and what an odd looking word that is when you really look at it!

The first part is obvious enough: Latin "ad-", which either means "from" or is an intensifier, converted into "ab-" because that is what we do before the letter ess. But what about that surd?

I couldn't tell because "surd" is actually a word referring to a kind of abstruse mathematical expression involving repeatedly extracted roots of irrational numbers, and I couldn't imagine what this might have to with absurdity, except for the obvious fact that such a thing is absurdly distant from most people's experiences of mathematics.

Well, as you may have guessed, the "-surd" in "absurd" is in fact the same as the mathematical surd, or at least they're from the same place: Latin "surdus", "deaf, mute". The reasoning goes that someone who is deaf and mute has a hard time making himself understood to hearing people, and so something which is absurd is likewise incomprehensible and senseless. A surd is so called because in the original Arabic, an irrational number was called "inaudible" (in contrast to the "audible" rational numbers), this eventually became in Arabic "asamm", "deaf or mute", and this was translated directly into Latin "surdus". All very strange, but that's mathematicians for you.