The Collaborative International Dictionary of English v.0.48:

Tough \Tough\, a. [Compar. Tougher; superl. Toughest.] [OE.
   tough, AS. t[=o]h, akin to D. taai, LG. taa, tage, tau, OHG.
   z[=a]hi, G. z[aum]he, and also to AS. getenge near to, close
   to, oppressive, OS. bitengi.]
   1. Having the quality of flexibility without brittleness;
      yielding to force without breaking; capable of resisting
      great strain; as, the ligaments of animals are remarkably
      tough. "Tough roots and stubs. " --Milton.
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   2. Not easily broken; able to endure hardship; firm; strong;
      -- of objects and people; as, tough sinews. --Cowper.
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            A body made of brass, the crone demands, . . .
            Tough to the last, and with no toil to tire.
                                                  --Dryden.
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            The basis of his character was caution combined with
            tough tenacity of purpose.            --J. A.
                                                  Symonds.
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   3. Not easily separated; viscous; clammy; tenacious; as,
      tough phlegm.
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   4. Stiff; rigid; not flexible; stubborn; as, a tough bow.
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            So tough a frame she could not bend.  --Dryden.
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   5. Severe; violent; as, a tough storm. [Colloq.] " A tough
      debate. " --Fuller.
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   6. Difficult to do, perform, or accomplish; as, a tough job.
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   7. Prone to aggressive or violent behavior; rowdyish; -- of
      people, or groups; as, a tough neighborhood; a tough
      character.
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   To make it tough, to make it a matter of difficulty; to
      make it a hard matter. [Obs.] --Chaucer.
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