The Collaborative International Dictionary of English v.0.48:

Subside \Sub*side"\, v. i. [imp. & p. p. Subsided; p. pr. &
   vb. n. Subsiding.] [L. subsidere; sub under, below + sidere
   to sit down, to settle; akin to sedere to sit, E. sit. See
   Sit.]
   1. To sink or fall to the bottom; to settle, as lees.
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   2. To tend downward; to become lower; to descend; to sink.
      "Heaven's subsiding hill." --Dryden.
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   3. To fall into a state of quiet; to cease to rage; to be
      calmed; to settle down; to become tranquil; to abate; as,
      the sea subsides; the tumults of war will subside; the
      fever has subsided. "In cases of danger, pride and envy
      naturally subside." --C. Middleton.
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   Syn: See Abate.
        [1913 Webster] Subsidence