The Collaborative International Dictionary of English v.0.48:

Dangerous \Dan"ger*ous\, a. [OE., haughty, difficult, dangerous,
   fr. OF. dangereus, F. dangereux. See Danger.]
   1. Attended or beset with danger; full of risk; perilous;
      hazardous; unsafe.
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            Our troops set forth to-morrow; stay with us;
            The ways are dangerous.               --Shak.
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            It is dangerous to assert a negative. --Macaulay.
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   2. Causing danger; ready to do harm or injury.
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            If they incline to think you dangerous
            To less than gods.                    --Milton.
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   3. In a condition of danger, as from illness; threatened with
      death. [Colloq.] --Forby. Bartlett.
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   4. Hard to suit; difficult to please. [Obs.]
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            My wages ben full strait, and eke full small;
            My lord to me is hard and dangerous.  --Chaucer.
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   5. Reserved; not affable. [Obs.] "Of his speech dangerous."
      --Chaucer. -- Dan"ger*ous*ly, adv. --
      Dan"ger*ous*ness, n.
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WordNet (r) 3.0 (2006):

dangerousness
    n 1: the quality of not being safe [ant: safeness]