To hide, cover, or conceal something, either partially or in full. He thinks he can just mask out the smell in the bathroom with that horrible deodorant spray, but it just makes everything worse. We've planted trees around the perimeter of our property to mask it out from the neighbors.
mask something out
to conceal or cover part of something from view. The trees masked the city dump out, so it could not be seen from the street. The trees masked out the dump.