Materialism

I got this from the Online Etymology Dictionary:

Materialism is 1748 as a philosophy that nothing exists except matter (from Fr.); 1851 (in Hawthorne) as "a way of life based entirely on consumer goods."

Ask Marx's neighbors.

Lots of words have different meanings or connotations in different contexts of usage. This is a normal feature of English and (I very much suspect) all natural languages.

That said, the meanings of "materialist" as applied to Marxist philosophy and American culture are not so very different. In both cases it means that only material things and material well-being are valued, and spiritual things are not. The connotations are different, however. Marxists, however, regard their materialism as a good thing (because they think the spiritual is unreal, and talk of spiritual values is just a trick used by the powerful to justify their power and privilege to themselves and to others), whereas people who use "materialist" to describe American (or other capitalist) culture usually mean to imply that it is a bad thing because it means that people recognize no "higher" values that might temper their greed and the ways in which they exploit one another in order to satisfy that greed. Of course, as far as Marx was concerned, the greed and exploitation was not a result of materialism as such, but of the capitalist economic system. A belief in spiritual values might take some of the edge off the nastiness inherent in capitalism, but, as he saw it, it would be better if people recognized that such values were a delusion, because this would help them to recognize the full horror of capitalism, and thus the need to change to a different sort of economic system.