Just by chance I sometimes come across a word that in nothing betrayed me it's meaning. Most of the time I have a guess in some direction, even if it proves to be the wrong one.
This one caught my eye on a random dictionary page ;

sidereal
1634, "of or pertaining to the stars," earlier sideral (1594), from Fr. sidereal (16c.), from L. sidereus "starry, astral," from sidus (gen. sideris) "star, constellation," probably from PIE base *sweid- "to shine" (cf. Lith. svidus "shining, bright").

I didn't see the starry or astral connection in any way. It looked like sidderaal, which in fact means 'electric eel'. but I knew that was nonsense. Surprised to see what it really means.

Yeah. In English we don't usually use that sidus element productively either. Mehbe tsuwm can come up with some words we've all known and loved that fit the bill.

sidereal

I've only run across this word in scattered works of science fiction and astrological texts. And, of course, I once dreamed that I wrote a book called Sidereus Nuncius (link). It was about the beneficial effect that txting was having on the English language.

> sidereal

when I took an astronomy class in college, this was a common word. especially as Sidereal Time

You made it to Nuncle at least. I've read Galileo's Daughter some years ago. Even for non scientifics like me a captivating book.

sidderaal

Thanks for that word, Bran. It took me through a couple or three dictionaries in fine fettle. Dutch sidderaal 'electric eel' related to sidderen 'to tremble, shake, quake'; cf. German zittern, Zitterfisch 'electric eel', English (dialectal) titter 'to shake, falter', teeter (as in teeter-totter, i.e., see-saw). English shudder is perhaps from a different Dutch verb schudden (cf. German schütteln). Something reduplicative and onomatopoeic is going on here: shiver, quiver, tremble, teeter, toddle, toodle-oo, etc.

[Added some more info from Bran.]

"Dim and wonderful is the vision I have conjured up in my mind of life spreading slowly from this little seed-bed of the solar system throughout the inanimate vastness of sidereal space. But that is a remote dream."
— H. G. Wells, War of the Worlds
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sider(o)- combining form (from Gk sideros) iron (cf. siderism, siderite)
sidero- combining form (from L. sidus) star (cf. sidereal, sideromancy, siderostat)

The Dutch one is schudden.

That's a wonderful Wells quote.