incidence
/ˈɪnsɪdəns/noun
1
- the occurrence, rate, or frequency of a disease, crime, or something else undesirable（疾病、犯罪等的）发生, 发生率：
an increased incidence of cancer.
癌症增长的发病率。
1.1
- the way in which the burden of a tax falls upon the population（民众的）税务负担：
the entire incidence falls on the workers.
税务统统落在工人头上。
2
- mass noun Physics the intersection of a line, or something moving in a straight line, such as a beam of light, with a surface【物理】入射。
词源
late Middle English (denoting a casual or subordinate event or circumstance)： from Old French， or from medieval Latin incidentia, from Latin incidere 'fall upon， happen to' （see INCIDENT）. Sense 1 dates from the early 19th cent.