The Arabic word for Earth is الْأَرْضِ / l-arḍi.
This comes from the root ا ر ﺽ and has the following derivative meanings:
ا ر ﺽ : to rotate; bring forth herbs; that which rotates; earth; land; city; country; ground
As shown above, one of the meanings of this root means to rotate, which is exactly what the Earth does.
Additionally, the Quran in several verses discusses the orbit of the planets.
[21:33] And He is the One who created the night and the day, and the sun and the moon; each floating in its own orbit.
وَهُوَ الَّذِي خَلَقَ الَّيْلَ وَالنَّهَارَ وَالشَّمْسَ وَالْقَمَرَ كُلٌّ فِي فَلَكٍ يَسْبَحُونَ
The word for orbit is فَلَكٍ / falakin, this word comes from the root: ف ل ك and has the corresponding derivative meanings:
ف ل ك : to be round; ships; ark; the orbit of a celestial body; pivot; axis
Some people argue that since this is the same root as the word for ship, that this does not mean “orbit” but instead just means to “sail”. What is interesting about this verse and specifically this expression ” كُلٌّ فِي فَلَكٍ ” which would be translated as “each in orbit” is that this phrase is a palindrome: a phrase that reads the same forward and backward. The significance of this is as if the letters are orbiting around one another like is being described in the verse itself.
Additionally, we read the following verse more about the orbit of the Earth.
[39:5] He created the heavens and the earth truthfully. He rolls the night over the day, and rolls the day over the night. He committed the sun and the moon, each running for a finite period. Absolutely, He is the Almighty, the Forgiving.
خَلَقَ السَّمَاوَاتِ وَالْأَرْضَ بِالْحَقِّ يُكَوِّرُ الَّيْلَ عَلَى النَّهَارِ وَيُكَوِّرُ النَّهَارَ عَلَى الَّيْلِ وَسَخَّرَ الشَّمْسَ وَالْقَمَرَ كُلٌّ يَجْرِي لِأَجَلٍ مُسَمًّى أَلَا هُوَ الْعَزِيزُ الْغَفَّارُ
This verse uses the expression “يُكَوِّرُ الَّيْلَ عَلَى النَّهَارِ وَيُكَوِّرُ النَّهَارَ”.
This verse clearly informs us that the Earth is round. The Arabic for “He rolls” (Yukawwir) is derived from the Arabic word for “ball” (Kurah). This verse is informing us that the Earth is rolled in order to achieve night and day. Since the Earth is not exactly round, a specific reference to its shape is given in 79:30.
In the following verse, we learn more about the orbit of the heavenly bodies according to the Quran.
[31:29] Do you not realize that GOD merges the night into the day and merges the day into the night, and that He has committed the sun and the moon in your service, each running in its orbit (specific course) for a specific life span, and that GOD is fully Cognizant of everything you do?
أَلَمْ تَرَ أَنَّ اللَّهَ يُولِجُ الَّيْلَ فِي النَّهَارِ وَيُولِجُ النَّهَارَ فِي الَّيْلِ وَسَخَّرَ الشَّمْسَ وَالْقَمَرَ كُلٌّ يَجْرِي إِلَىٰ أَجَلٍ مُسَمًّى وَأَنَّ اللَّهَ بِمَا تَعْمَلُونَ خَبِيرٌ
Many people think that the Sun is stationary while the Earth revolves around the sun, but the Sun is also moving in an orbit around the Milky Way Galaxy. Below is a video animation showing that not only is the Earth and other planets revolving around the Sun, but the Sun itself is pursuing its own course as well.
This is the significance of stating in the above verse that “each running in its orbit (specific course)“. The word in this verse used for “orbit” or “specific course” this time is يَجْرِي. This word comes from the following root with the corresponding derivative meanings:
This indicates that not only are each running in their own pursuit, but that they are also commissioned to follow one another.
This is further confirmed in the following verse, where we see that not only is the moon revolving around the Earth, but by default it is also revolving and following the sun.
[36:40] The sun is never to catch up with the moon—the night and the day never deviate—each of them is floating in its own orbit.
لَا الشَّمْسُ يَنْبَغِي لَهَا أَنْ تُدْرِكَ الْقَمَرَ وَلَا الَّيْلُ سَابِقُ النَّهَارِ وَكُلٌّ فِي فَلَكٍ يَسْبَحُونَ