An example of someone who may attempt to assimilate a country's customs is an immigrant.
An example of something one might assimilate is the dialect of a different region after spending much time there.
An example of something body might assimilate is milk.
Origin of assimilate
- Middle English assimilaten from Latin assimilāre assimilāt- to make similar to ad- ad- similis like sem-1 in Indo-European roots
From American Heritage Dictionary of the English Language, 5th Edition