n.

1. 落下；影響；落下（或影響）方式[U][S1]
2. 發生率；影響範圍[U][S1]
   There's a high incidence of heart disease there.

   那個地方心臟病的發病率很高。

3. 【物】射入；入射角
4. 【數】關聯；接合

n.

1. the occurrence, rate, or frequency of a disease, crime, or other undesirable thing.
2. Physics  the intersection of a line, or something moving in a straight line, such as a beam of light, with a surface.
3. the way in which the burden of a tax falls upon the population.