'an' is used when the sound of the next letter is the sound of a vowel, so in the case of eN-E-S, 'an' is correct. In english multiple vowels in a row cause yo

'an' is used when the sound of the next letter is the sound of a vowel, so in the case of eN-E-S, 'an' is correct. In english multiple vowels in a row cause you to take a pause, which is why the -n is added Worth noting, the other posters are correct in saying that 'a snezz' or 'a ness' is also correct.