What does the word bellyache mean?

When you bellyache someone, you complain in a whining manner. In other words, you sound as if you are moaning.

Here are a few examples.

Whenever I run into Pankaj, he bellyaches about all the work he has to do.

Some of your friends tell me that you bellyache about a lot of things.

A person who is constantly complaining is a bellyacher.