The Collaborative International Dictionary of English v.0.48:

Canker \Can"ker\ (k[a^][ng]"k[~e]r), n. [OE. canker, cancre, AS.
   cancer (akin to D. kanker, OHG chanchar.), fr. L. cancer a
   cancer; or if a native word, cf. Gr. ? excrescence on tree, ?
   gangrene. Cf. also OF. cancre, F. chancere, fr. L. cancer.
   See cancer, and cf. Chancre.]
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   1. A corroding or sloughing ulcer; esp. a spreading
      gangrenous ulcer or collection of ulcers in or about the
      mouth; -- called also water canker, canker of the
      mouth, and noma.
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   2. Anything which corrodes, corrupts, or destroy.
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            The cankers of envy and faction.      --Temple.
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   3. (Hort.) A disease incident to trees, causing the bark to
      rot and fall off.
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   4. (Far.) An obstinate and often incurable disease of a
      horse's foot, characterized by separation of the horny
      portion and the development of fungoid growths; -- usually
      resulting from neglected thrush.
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   5. A kind of wild, worthless rose; the dog-rose.
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            To put down Richard, that sweet lovely rose.
            And plant this thorm, this canker, Bolingbroke.
                                                  --Shak.
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   Black canker. See under Black.
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