Dangerous, a.
Etymology: [OE., haughty, difficult, dangerous, fr. OF. dangereus, F. dangereux. See Danger.]
1. Attended or beset with danger; full of risk; perilous; hazardous; unsafe. Our troops set forth to-morrow; stay with us; The ways are dangerous. Shak. It is dangerous to assert a negative. Macaulay.
2. Causing danger; ready to do harm or injury. If they incline to think you dangerous To less than gods. Milton.
3. In a condition of danger, as from illness; threatened with death. [Colloq.] Forby. Bartlett.
4. Hard to suit; difficult to please. [Obs.] My wages ben full strait, and eke full small; My lord to me is hard and dangerous. Chaucer.
1 more senses
5. Reserved; not affable. [Obs.] "Of his speech dangerous." Chaucer. -- Dan"ger*ous*ly, adv. -- Dan"ger*ous*ness, n.
Shades of meaning
Fernald has no entry of its own for dangerous; he lists it under formidable.
Where he writes about it:
Formidable is a word of more dignity than dangerous, and suggests more calm and collected power than terrible; formidable is less overwhelming than tremendous. — from formidable
A loaded gun is dangerous; a park of artillery is formidable; a charge of cavalry is terrible; the full shock of great armies is tremendous. — from formidable
A dangerous man is likely to do mischief, and needs watching; a formidable man may not be dangerous if not attacked; an enraged maniac is terrible; the force of ocean waves in a storm, and the silent pressure in the ocean depths, are tremendous. — from formidable