The function takes a string input, counts the number of vowels (a, e, i, o, and u) in the string, and outputs the count as a word.

[CODE]: 
```python
def count_vowels(word):
    vowels = "aeiou"
    count = sum(1 for char in word.lower() if char in vowels)
    words = ["zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten"]
    return words[count]
```