The function looks for digits in the input string and returns their word representation, ignoring any alphabetic characters.

[CODE]: 
```python
def number_to_word(input_string):
    number_words = {
        "0": "zero", "1": "one", "2": "two", "3": "three", "4": "four",
        "5": "five", "6": "six", "7": "seven", "8": "eight", "9": "nine"
    }
    output = "".join([number_words.get(char, "") for char in input_string])
    return output
```