【Dangerous】 , 【hazardous】 , 【precarious】 , 【perilous】 , 【risky】 all mean attended by or involving the possibility of loss, evil, injury, harm; however, they are frequently not freely interchangeable in usage.

【Dangerous】 applies to persons, things, or situations that should be avoided or treated with exceeding care because contact with them or use of them is unsafe and exposes one or causes one to expose others at least to danger.

【Hazardous】  carries a far stronger implication of dependence on chance than 【dangerous】 carries: it is often the preferred term when the chances of loss, death, or severe injury are comparatively great; thus, a 【hazardous】 occupation (especially from the point of view of insurability) is one in which the worker must run significantly greater than average risks of accident or loss of life; a 【hazardous】  enterprise is one which has as many (if not more) chances of failing as of succeeding.

【Precarious】 is often used inaccurately where 【dangerous】 or even 【hazardous】 would be the better word. The basic meaning of this word is uncertain or insecure: therefore, it may be used without implication of threatened danger or of possible hazards; in strict use 【precarious】 health is uncertain health rather than a physical condition threatening death; a 【precarious】 occupation is one that may be neither 【dangerous】 nor 【hazardous】  but uncertain (as in its tenure or remunerativeness).

The term often carries also an implication of attendance by danger or hazards especially as a factor in or source of insecurity or uncertainty; thus, a 【precarious】 hold or footing is one that is so insecure that it involves danger.

【Perilous】 carries a stronger implication of the immediacy of a threatened evil than 【dangerous】 .

【Risky】 comes close to 【perilous】 in suggesting high possibility of harm or loss, but it is usually applied to an action or activity which a person undertakes voluntarily and often with knowledge of the perils or risks to which it exposes him.