Define 'Assimilation' as an noun?

The complete and total absorption of a element into a dominent element or feature.

I guess as a noun it would be the act of something like a culture being completely absorbed by a larger force.

ex: um...like native american culture has been completely assimilated into modern popular culture

Assimilation means blending in with others. For example:

The Australian government is encouraging assimilation in new migrants in Australia.

The process whereby a minority group gradually adopts the customs and attitudes of the prevailing culture. (Gradually, as in "over two or three generations".)

I think putting "completely" in there is not warranted. America expected new immigrants to assimilate into our society: That meant we expected them to learn to speak American, but no one expected them to eliminate their accents or even to speak perfect English. Until the Sixties we figured they'd wear American clothes, though we loved going to their national festival day and seeing them in their Old World dress. Sometimes they Americanized their names but we didn't expect all of them to be named Smith, and no one griped if they didn't name their kids John and Mary but Seamus and Diarmid. And quite frankly, if we went over to their house for dinner and found a meat loaf on our plates, we'd feel deprived (in their over-kindness) that we didn't get blini.