The Collaborative International Dictionary of English v.0.48:

Cumbrous \Cum"brous\ (k?m"br?s), a.
   1. Rendering action or motion difficult or toilsome; serving
      to obstruct or hinder; burdensome; clogging.
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            He sunk beneath the cumbrous weight.  --Swift.
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            That cumbrousand unwieldy style which disfigures
            English composition so extensively.   --De Quincey.
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   2. Giving trouble; vexatious. [Obs.]
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            A clud of cumbrous gnats.             --Spenser.
      -- Cum"brous*ly, adv. -- Cum"brous*ness, n.
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