a.

1. 有意义的；意义（或意味）深长的
   I noticed that there has been a significant change on you.

   我注意到你身上发生了有意义的改变。

2. 表示……的[+of]
   Smiles are significant of pleasure.

   微笑表示愉快。

3. 重要的，重大的；值得注意的
   This is one of the most significant studies of the subject.

   这是对该课题最重要的研究之一。

4. 显著的；有效的；非偶然的

n.【古】[C]

1. 有意义的事物
2. 标志，象征

adj.

1. having an unstated meaning; indicative of something.
2. extensive or important enough to merit attention.
3. Statistics  relating to or having significance.