This word is not loud. It’s not just that it’s not loud minus a letter; it’s not just that it’s pronounced /u:d/ (the spelling is a French-influenced one; you can also see it as ud); it’s also that what it names is not unusually loud. It can be somewhat loud or very quiet, but you are unlikely to want to stop your ears due to the loudness of the noise it produces.
What is it? It is not some kind of dictionary (like the OED) nor a long-term contraceptive (that’s an IUD). It’s not an acronym at all. Nor is it a centuries-old colloquial way of saying would (you will see ’ould or ’ud, but not oud). It is, according to the OED, an instrument of the lute family. But if you look at the history, you may wonder whether it would be more sensible to call a lute an instrument of the oud family.
It’s not simply that the oud is the more ancient. It’s that lute comes from Arabic al-ʿūd, ‘the oud’. (Where does ʿūd come from? Well, it’s Arabic for ‘wood’, and the instrument is made of wood – and whatever you use for the strings. Some people think the word in this case may have been borrowed from Persian, but that’s not universally agreed).
There are two general kinds of ouds: Turkish and Arabic; the Arabic kind has several sub-types. The main difference, though, is that the Arabic oud is a bit larger than the Turkish oud.
Of course you can play all sorts of things on an oud; it has enough strings, and enough of a range, that you can really play the music of your choice – especially since there are no frets on it, so you can choose your scale. But it’s associated with the music that is normally played on it: Arabic and Turkish music of various kinds. I happen to like this kind of music quite well, and I think it’s very good for reading or studying or writing to. I ought to know – when I was in grad school at Tufts, I spent a lot of time in their music library listening to CDs from all over the world, and Arabic music was one kind I could count on for getting quite a bit done while enjoying what I was hearing. It is – for me – simultaneously relaxing, enjoyable, and mentally stimulating. Sort of like Arabic or Turkish coffee, but without the shakes. (Now I look at oud and I see a small coffee cup – from above o and the side u – and an oud, d.)
Your results may vary, of course. But here are a couple of performances on the oud, one Arabic and one Turkish. If you like them, there are plenty more:
I have this idea to cross the Aeolian harp with the oud, just so I could call it an oud-wind. But I probably won’t.