The form,use, and meaning of words change over time. For instance, try searching ETHNICITY and then try ETHNIC. See the OED (Oxford English Dictionary) to see how words have been used in different eras.
For searches that return too many hits, remember all the ways you can narrow your search by using options in the right-hand margin on your results page:
by date (choose fewer decades)
by document type (article, or advertisement, or fiction, or...)
and by publication title or publication subject
Use the Modify Search button to go back and add or change terms in your original search