In Greek, Jesus is Ἰησοῦς (pronounced, ee-ay-sooce). In early Latin an i could be used either as a vowel (short or long) or as a consonant (as a y). Thus, the Latin, Iēsus, was pronounced yay-sus. In medievil Latin, the letter j was used to replace i‘s that where being used as consonants. The j was pronounced as a y. Hence, in modern Spanish, ‘Jesus’ is still pronounced Yay-sooce. In English, however, the j was hardened and, consequently, ‘Jesus’ is pronounced Gee-sus.