The Collaborative International Dictionary of English v.0.48:

Inanity \In*an"i*ty\, n.; pl. Inanities. [L. inanitas, fr.
   inanis empty: cf. F. inanit['e]. See Inane.]
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   1. Inanition; void space; vacuity; emptiness.
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   2. Lack of seriousness; aimlessness; frivolity.
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   3. An inane, useless thing or pursuit; a vanity; a silly
      object; -- chiefly in pl.; as, the inanities of the world.
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