כּוּשׁ may be the Hebrew name for Ethiopia, but כּוּשִׁי just means a black man and is roughly equivalent in both meaning and usage to “the N-word”.

http://mordochai.tripod.com - פרופ' מָרְדֳּכַי בֶּן-צִיּוֹן, יְרוּשָׁלַיִם, אֶרֶץ יִשְׂרָאֵל