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Two objects are termed "counter-rotating", if they rotate in opposite direction, i.e. one rotates clockwise while the other rotates counter-clockwise. (see: counter-rotating propellers)

Is there also a word for objects rotating in the same direction? I though of "corotating", which however seems to have different meanings.

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    Corotating or (co-rotating) seems correct to me. Perhaps you misunderstand the flexibility of the definition. merriam-webster.com/dictionary/corotate
    – user22542
    Commented Apr 13, 2021 at 11:19
  • @user22542 so despite the flexibility, its meaning will be clear, if I use it in the same sentence as co-rotating. I also wondered, why oxford dictionnary does not list "corotate", but did not look in Merriam-Webster. Thanks a lot!
    – Libavi
    Commented Apr 13, 2021 at 11:33
  • 'Rotating in the same sense.'
    – Edwin Ashworth
    Commented Apr 14, 2021 at 10:49
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    @Libavius - I would definitely understand your (specific) meaning of "co-rotating" from the context in your description, if nothing else. It is very true that various dictionaries (much like people) are not always on the same page (pun intended). I thought you might also be able to use the prefix "syn-" to the same effect (such as "syn-rotational" for example), but it seemed awkward to me. But, you might consider something like "syn-directional rotation". I hope this helps.
    – user22542
    Commented Apr 14, 2021 at 22:58

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Your dictionary search should have revealed corotate and corotational

corotate, intransitive verb: to rotate in conjunction with or at the same rate as another rotating body

Merriam Websters

Also see

Corotational: That rotates in conjunction with another body

Wikipedia

Oxford Reference gives the example of two bodies spinning about their common centre of mass, and therefore necessarily in the same clockwise or anti-clockwise way.

Where one body orbits another, the circumstance in which one or both bodies have an axial rotation period the same as the orbiting body's revolution period. The co-rotating body therefore keeps one face permanently turned towards the other, as in the case of the Moon facing the Earth. In the case of Pluto and its satellite Charon, both bodies are in co-rotation and so each keeps the same face turned to the other. See also spin–orbit coupling; synchronous rotation.

Oxford Reference

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    Does 'in conjunction with' demand 'in the same direction'?
    – Edwin Ashworth
    Commented Apr 13, 2021 at 18:51
  • @EdwinAshworth Good Point. Cambridge has conjunction as "the situation in which events or conditions combine or happen together". I rather took this as the rotations happening together, that is - in the same sense. Perhaps there are better definitions of "corotational" than in the Wikipedia.
    – Anton
    Commented Apr 13, 2021 at 22:00
  • @EdwinAshworth I have added the Oxford reference to try to deal with your point.
    – Anton
    Commented Apr 13, 2021 at 22:29
  • @Anton the Oxford reference is actually another reason why I doubted that corotational is correct here. If you read it carefully, it describes specifically that the rotation of the moon around its own axis is at exactly the same speed as the rotation of the moon-earth system around its common center. Thus, corotational here is about the same speed, while the directions of both rotations (moon around itself and moon around earth) are actually opposite. Your Merriam Websters and Wikipedia references also refer more to the speed than to the direction of rotation.
    – Libavi
    Commented Apr 19, 2021 at 11:39
  • @Libavius I was loth to stray into too much physics but I am compelled to remark your confusion about speed (which is a merely a scalar quantity with no direction), and your omission of velocity (a vector with a speed and a direction). You also omit to mention angular velocity, which is a vector that has the same direction for the earth moon corotating bodies. The speeds of moon and earth are not the same relative to the centre of mass; the velocities at any instant are directionally opposed; the angular velocities have the same direction and the bodies are thus corotating.
    – Anton
    Commented Apr 19, 2021 at 22:15

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