Wiktionary suggests that moon comes from PIE meh (measure), likely because the full moon was the measure of a month.
On the other hand, lunar is proposed to ultimately derive from PIE lewksneh, “the shining one”.
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The bigger question is whether the Sun revolves around Earth. No matter what, I don’t see why the system with the Sun (or alternatively center of gravity) in the center should have precedence over the system with Earth in the center. Except that we like it this way.
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I’ve actually never thought about this and I’m a huge astronomy nerd. Thank you for pointing this out!
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I can’t tell if you’re being sarcastic.
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I always thought the moon is feminine in most languages/ cultures.
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No, not sarcastic. Because all the explanations don’t invalidate coordinate system with the Earth in the center. So in coordinate system with the Earth in the center, the Sun does revolve around it, doesn’t it. It should be a completely legitimate answer.
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Spin is a relative thing. If you fix the Earth as your center of reference, then the Sun spins around the Earth. If you fix the center of reference to be the center of mass in our solar system (which lies inside the sun), then the Earth spins around the Sun.
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Spin or revolve? They are different things in Greek, but maybe my English is betraying me.
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Doesn’t really matter, both apply 
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Earth-centric models have been widely used throughout history, but have the drawback of greatly complicating the modeling of the motions of the other planets relative to the Earth.
The sun is a natural choice for basing the frame of reference, since it has 99.8% of the mass in the solar system and thus gravitationally dominates the rest. Within a heliocentric model, the motions of the rest of the bodies are much simpler to explain and model.
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Moon and Sun trade genders in German. She reigns in the day, he at night.
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Y’all are much too smart for me, I was taught heliocentric model and that was it. 
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Oh, right. And I’ve been taught German. I’m actually ashamed, because I knew that. 
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Are we talking about reference systems in the context of relativity theory? Because in that case I believe it is important to note that the earth’s movement is accelerated due to the gravitational pull of the sun (among other forces). However the reference system must be non-accelerated.
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It’s opposite of the Greek mythology, where Helios is male and Selene is female.
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Fun fact, in modern Greek we also have another word for moon, “το φεγγάρι” (the light, of shorts), which is neutral.
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The same holds for the sun in reference to the milky-way, though. Or the milky-way in reference to any other galaxies. (And for the sun in reference to the solar system, although the sun is pretty static compared to the center of mass of the solar system)
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Since you’re pedant, you should agree that technically we should be able to choose any reference we want. And thus, since I want reference to be Earth, it’s entirely ok for me to say the Sun revolves around me.
Yeah, I mean in some sense we live in a reference system tied to our bodies that accelerate all the time. And the world doesn’t explode.
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The sun’s motion is also being accelerated by the gravitational pull from all of the planets.
I’m not intending to talk about anything related to relativity with my previous post. In fact, I’m envisioning the oversimplification that ignores the gravitational effects that make the sun wobble.
If we want to talk about relativity, we’d have to distinguish between inertial and non-inertial (e.g., rotating) reference frames.
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I’m not arguing against that. In fact, I agree that our lives are dominated by the perception of the sun revolving around us (e.g., the day/night cycle) and it matters little whether we try to explain that with a heliocentric or Earth-centric model.
However, I am trying to explain why some might favor the heliocentric model, which seems to be your initial question of why the sun could take precedence as the center.
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