Kāfir is an Islamic term of Arabic origin used by Muslims to refer to non-Muslims who deny the God of Islam, reject his authority, or do not accept the message of Islam as truth.
The Kafirs of Natal and the Zulu Country by Rev. Joseph Shooter
Goy is a term for a gentile, a non-Jew, sometimes in a pejorative sense. The word, of Hebrew origin, was adopted into English from Yiddish. It carries a similar meaning in Modern Hebrew.
A page from Elia Levita's Yiddish–Hebrew–Latin–German dictionary (16th century) including the word goy (גוי), translated to Latin as ethnicus, meaning heathen or pagan.