Can "Jewish" be considered an ethnicity?

No. "Jewish" is an adjective that can be applied to many things about the Jews. Jewish food, Jewish *ethnicities* ( note the plurality) Jewish jokes, Jewish law.

Speaking of Jewish law..that is the only critera the Jewish people use for establishing who is or isn't a Jew. Not ethnicity.

Judaism is the religion of the Jewish people. Jews have been of more than one ethnicity since the destruction of the First Temple. It's impossible to use an ethnicity to determine if someone is or isn't a Jew.

See the detailed explanations at the link below.

edit: I'll use Blue Light's answer to highlight what was wrong with it. There is indeed a Jewish religion, Judaism. But if someone just decides they believe "Jewish" that doesn't make them a Jew unelss they've become a member of the Jewish people according to Jewish law. There are many ethnicities of Jews and Jews of every ethnicity.

Both of those men were Jews according to the criteria of Jewish law established in the Torah ( the Hebrew Bible) Ethnicity didn't determine that Einstein was a Jew.

Einstein was a Jew because he qualified according to Jewish law to be considered a Jew. His professed concept of God was pantheistic, not the concept of a personal God of Torah....but he was a Jew because he was born to a Jewish mother and didn't adopt any other religion that would have been willful separation ( estrangement/apostacy) from the Jewish people. Einstein's "ethnicity" was Ashkenazi.

Sammy Davis Jr. was a Jew because he qualified according to Jewish law to be considered a Jew after his formal conversion to Judaism. His ethnicity was Afro-American.

Only two ways to be a Jew 1) born to a Jewish mother ( of any race or ethnicity) 2) formal conversion to Judaism

those details are better explained at my link below and its references

I always ask people who want to insist that "Jewish" is an ethnicity..WHICH one of the ethnicities of Jewish people would you have Jews designate as "the" Jewish ethnicity to the exclusion of all others? It simply isn't logical to claim a single ethnicity for the Jewish people. I also believe that to insist that an ethnicity can *determine if one is or isn't Jewish* (a Jew), one is disrespectful to the right of the world's Jewish people to maintain our own laws of self-determination and identity. While this list isn't all inclusive, you have ethnicities of Ashkenazi, Mizrahi, Sephardi, Beta Yisrael, Yemeni, Bukharan,Cochin, and Kaifeng Jews, oh..and there has even been designated an ethnic distinction of Southern Delta Jews in the United States.

It should now be crystal clear. No, there is no single Jewish ethnicity and ethnicity doesn't determine if one is a Jew.

There are Jews of all ethnicities. Non-practicing Jews are still Jews because that's how Jewish law works.

Of course. Non-religious Jewish folks still consider themselves Jewish.

There's a Jewish religion and a Jewish ethnicity. They're not always the same. Einstein was Jewish ethnically, but religiously, he was a pantheist/deist.

Sammy Davis, Jr. was Jewish religiously, but he was black ethnically.

No, "Jewish" just refers to someone who practices Judaism, regardless of what Hitler and a few other notables have tried to contend. There are Polish Jews, Russian Jews, English, French, Italian and Israeli Jews. There are Ethiopian Jews. It's just a religion. Would you say there is a "Catholic race?"

Yes. "Jewish" can either refer to the religious beliefs of Judaism, which anyone of any ethnicity can adhere to if they so choose, or it can refer to the decedents of the ancient Israelites, the original Jewish people.

No, there are different type of ethnic Jews like Sephardic, Ashkenazi, Mizrahi, etc.

Nope, but some people will say they are just "Jewish."