What's the context of the use of the word?

It means different things according to my Google search.  One is the master paint scheme used to identify how a product gets painted.  Example:  a plastic figure is painted in the colors that the vendor wants.  The figure is sent to the factory.  They copy it.  It's the paintmaster scheme.

There are other meanings.  One is a mestre who can do lanternagem like a carioca.  It depends on what context you are using.