You can find the information you desire more quickly, if you use a hard copy or online dictionary.
Here is the definition from an online dictionary of "ethnic," which I got after looking up "ethnicity":
Main Entry: eth·nic
Etymology: Middle English, from Late Latin ethnicus, from Greek ethnikos national, gentile, from ethnos nation, people; akin to Greek Ethos custom —more at SIB
Date: 15th century
1 : HEATHEN
2 a : of or relating to large groups of people classed according to common racial, national, tribal, religious, linguistic, or cultural origin or background <ethnic minorities> <ethnic enclaves> b : being a member of an ethnic group c : of, relating to, or characteristic of ethnics <ethnic neighborhoods> <ethnic foods>
It refers to groups that share a "style of life."
I searched Google under the key words "ethnicity" to get these possible sources:
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search.
I hope this helps. Thanks for asking.