the word adj "كورت" "kuwwirat" from the root verb "kawwar" "كور", this word source came from Quran as some arabic webs says.
in surat al takweer it's mentioned as adj and as something will be done to the sun in the future , if you try to translate the word "كورت" "kuwwirat" in google translation it will be football
. it's mentioned as a verb in surat i zumar verse 5 "yokawwer" "يكور". we don't use this word much except in the adj FootBall "كورة" "koora" and soccer, and we use verb kawwar when want to make something like ice ball , and meat ball and hide something inside it, such as meat ball stuffed with nuts and we calls them "korraat al lahm" meat balls. some arabs uses it when they rounding their head with a turban.
i have this website also for full information about this word if someone can translate it.
http://www.almaany.com/ar/dict/ar-ar/%D9%83%D9%88%D8%B1%D8%AA/so i even use tafseer for it as you do , maybe it needs a muslim astrologist to understand it.
I'm biased to this translation for these 2 verses specifically.
Shakir:(81:1) When the sun is covered,
Shakir:Verse (39:5) ....,He makes the night cover the day and makes the day overtake the night, and He has made the sun and the moon subservient; each one runs on to an assigned term; now surely He is the Mighty, the great Forgiver.