In obsolete terms the difference between mass and combine
is that
mass is precious metal, especially gold or silver while
combine is to bind; to hold by a moral tie.
In transitive terms the difference between mass and combine
is that
mass is to form or collect into a mass; to form into a collective body; to bring together into masses; to assemble while
combine is to have two or more things or properties that function together.
In intransitive terms the difference between mass and combine
is that
mass is to have a certain mass while
combine is to come together; to unite.
As an adjective mass
is involving a mass of things; concerning a large quantity or number.
As a proper noun Combine is
london Underground.