contagion（n.）
14世纪晚期，“一种传染病； 一种有害或腐败的影响”，源自古法语 contagion，直接源自拉丁语 contagionem（主格 contagio）“接触”，常常带有不良含义，“与身体或道德上不洁净的东西接触，传染病”，源自 contingere “接触”，来自 com “与，一起”（见 con-) + tangere “触摸”，源自 PIE 词根 *tag- “触摸，处理”。意思是“传染性接触或交流”始于1620年代。
A distinction between contagion and infection is sometimes adopted, the former being limited to the transmission of disease by actual contact of the diseased part with a healthy absorbent or abraded surface, and the latter to transmission through the atmosphere by floating germs or miasmata. There are, however, cases of transmission which do not fall under either of these divisions, and there are some which fall under both. In common use no precise discrimination of the two words is attempted. [Century Dictionary, 1897]
有时采用 contagion 和 infection 之间的区别，前者仅限于通过患病部位与健康吸收或磨损表面的实际接触传播疾病，后者则通过漂浮的细菌或瘴气在大气中传播。然而，有些传播情况不属于这两个部分，有些情况则属于两者。在常用中，不尝试精确区分这两个词。[世纪词典，1897]
该词起源时间：14世纪末