MEI-4

妹 = younger sister, girl

However, this morpheme is seldom used alone.

In the meaning 'younger sidter', the following is much more common:

妹妹 = mei(4)mei(-) = younger sister(s)

The duplicated version is used even when there is only one younger sister

In thw meaning 'girl', the following is possible, though not common:

妹子 = mei(4)zi(-) = a girl

辣妹 = la(4) mei(4) = a hot girl