"Jewish" gets used with the loose definition of "people who have been expelled from their homeland."
Judaism is the religion formed by the people who were expelled from Egypt. They left Egypt to settle in Israel and establish Judaism.
Over the years, Christianity and Islam gained a foothold in the region, until the UN shoved the inhabitants of Israel into Palestine.
Arguably, modern Palestinians, who largely practice Islam, are Jews.
This leads me to the question, is the term "antisemitic" specific to Judaism or does it cover other types of Jews?
Depending on the answer, you can call modern Israel antisemitic against Palestinian Jews, who want their homeland back, or at the very least to stop being oppressed in the place that they were exiled to. This would make anyone who supports Israel antisemitic.
Edit: Bonus funfact, there is almost perfect overlap on how "Jew" gets used and how "Gypsy" get used. The key difference is that Jews TEND to move from an origin to a destination. Gypsies TEND to have an era of transience. Some Jews get displaced more than once before they can lay down roots. Some Gypsies get displaced so many times that they just go full on nomad/caravan lifestyle and never really stop moving around.
"Gypsy" and "Jew" don't have hard universally accepted definitions, and both of them are derogatory terms. People who identified with (or who were identified as) either of the 2 were targeted equally during the Holocaust, Gypsies were just more efficient at getting the fuck out before being loaded into the trains.
You should never say "I really got Jewed/Gypped by that guy." Both are EXTREMELY offensive terms, and people got sent to ovens over those words being used on them. The Holocaust was not all about Judaic Jews.