The term כוש as a reference to a place is indeed biblical. And it's quite possible you grew up before it was a slur. But language shifts, and in 2020 using the

The term כוש as a reference to a place is indeed biblical. And it's quite possible you grew up before it was a slur. But language shifts, and in 2020 using the term כושי (kushi) to refer to a black person is not ok. Same for the term shvartze in Yiddish, referenced elsewhere in this thread. I grew up with this term in my vocabulary and no harm was meant. But I wouldn't say it today, at least not if I was speaking English otherwise. In a fully Yiddish conversation I'd cut the speaker slack, though, especially if the speaker comes from a relatively secluded community that isn't experiencung the same drift in language the rest of society is. Point is, context matters. You need to pay attention to how words change over time and how they'll be perceived by your audience.