26 June 2018


   Gibbous                                           Crescent

I recently listened to a podcast that mentioned a "waxing gibbous moon," and wondered about the definition and etymology.

In astronomical terms, gibbous moons precede and follow the full moon.  The etymology is from Middle English, from Latin gibbus (humped, hunched), probably cognate with cubō (bend oneself, lie down), Italian gobba (humpback), Greek κύφος (kýfos, humpback, bent), κύβος (kývos, cube, vertebra).

So the gibbous moon is "humped" but it's not the same as the crescent moon, which occurs in the other half of the cycle, around the new moon.

In medical terms, a gibbus deformity is a sharp angulation of the spine (image via), slightly different from the more gradual deformity of conventional kyphosis.


  1. Wonder how that worked with Edward Gibbons, the famous historian?

  2. To add to this: "Crescent" goes back to Latin crescere = "to grow", so technically only the waxing crescent (the Ↄ-shaped one, if you're in the northern hemisphere) should have that name; I guess the waning one (C-shaped in the north) would properly be something like a diminuent?

    Additional fun fact: If you know a little French, you can easily check which quarter the moon is in: Add a vertical line and you can turn the Ↄ shape into a p for premier = first quarter, while the C shape turns into a (lower case) d for dernier = last quarter.

    Oh, and of course they call a croissant that because that's its shape :)


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