hair of the dog

[Offroad]

Please, dear teachers and friends,

could you shed a light on this?

1) Hair of the dog.
What does that expression mean?

2) How do you call a person who is an adult but still acts like a child? Could one call her/him a childish person?

Many thanks in advance!

[bhaisahab]

1/. 'Hair of the dog' comes from 'A hair of the dog that bit you' meaning 'a little bit of what did you harm'. It is often used in connection with over indulgence in alcohol, after having drunk too much the night before, and feeling the worse for it, people would sometimes go for a drink in the morning to feel better.
2/. Childish is good.

[CHOMAT]

It was thought that taking a hair of the dog that bit you was a cure for rabies.
Today, tt has something to do with hangovers..