The function takes an input string and converts numbers into their corresponding words.

[CODE]: 
```python
def number_to_word(number_str):
    num_dict = {
        '1': 'one', '2': 'two', '3': 'three', '4': 'four',
        '5': 'five', '6': 'six', '7': 'seven', '8': 'eight',
        '9': 'nine', '0': 'zero'
    }
    result = ''
    for char in number_str:
        if char in num_dict:
            result += num_dict[char]
    return result
```

Feel free to test the function with other strings to further confirm its behavior.