noun

• (music) The lowness of a note.
• (physics) The phenomenon that, on earth, objects have weight; the similar phenomenon on other celestial bodies such as the moon.
  "Do you know that gravity is pulling at you, tugging at you, trying to drag you down, from the moment you awake in the morning till you tumble into bed at night?"
• (loosely, see usage notes) Gravitation, the universal force exercised by two bodies on each other by virtue of their masses.
• (physics) A law or laws of gravitation: any theory which attempts to account for the phenomena of weight and/or the mutual attraction of massive objects (Aristotelian gravity, Newtonian gravity).
  "Some of the most beautiful and thus appealing physical theories, including quantum electrodynamics and quantum gravity, have been dogged for decades by infinities that erupt when theorists try to prod their calculations into new domains. Getting rid of these nagging infinities has probably occupied far more effort than was spent in originating the theories."