a.

1. 第二的；第二位的
2. （教育、学校等）中等的[B]
   Virtually all secondary schools are in towns.

   几乎所有的中学都在城里。

3. 次要的；从属的，辅助的[（+to）]
   Many older people still believe that women's careers are secondary.

   许多年岁大一点的人仍然认为妇女的职业生涯并不那么重要。

4. 第二手的，间接的
5. 【医】继发性的；第二期的
6. （颜色）次的，合成的
7. 【语】次要的；次重音的

n.[C]

1. 副手，次要人物；次要的东西
2. 代表，代理人
3. 【美】【橄】第二防线

adj.

1. coming after, less important than, or resulting from something primary.
2. relating to education for children from the age of eleven to sixteen or eighteen.
3. of or denoting the output side of a transformer or other inductive device.
4. Chemistry  (of an organic compound) having its functional group on a carbon atom bonded to two other carbon atoms.
   ▸derived from ammonia by replacement of two hydrogen atoms by organic groups.
5. (Secondary) Geology  former term for Mesozoic.
6. (of a cell or battery) having a reversible chemical reaction and therefore able to store energy.