Here's why:
* Short vowel sound: In "vanish", the "a" makes a long "a" sound, similar to the "a" in "day". Short vowels are typically found in words like "cat", "dog", "hot", where the vowel sound is short and sharp.
* The "i" sound: The "i" in "vanish" has a short vowel sound, as in "fit" or "bit".
Therefore, "vanish" does not contain a short vowel "a".