根据汉语补充和首字母提示写出单词

根据汉语补充和首字母提示写出单词
1、To be important or have an important effect on sb.首字母m
2.something that is known about by only a few people and not told to others.首字母s
3.one of the periods of time that the school or university year is divided into.首字母t