Pardon the copy/paste:

Antisemitism is understood to mean prejudice against Jews.

Semitic languages is the formal name for the branch of the Afroasiatic language family that includes modern Hebrew, Arabic, Amharic and ancient languages like Akkadian and Phoenician.

Semitic people isn't a term that anyone uses for real, but if they did it would refer to peoples who have traditionally spoke semitic languages.

It's frustrating that the term antisemitism refers to prejudice against only a specific subset of the peoples who would fall under the semitic label. But deliberately misunderstanding the term antisemitism is also quite frustrating.