The function takes a string input and returns the word representation of the number of characters in the input string.

[CODE]:
```python
def string_length_word(input_string):
    num_to_words = {
        1: "one",
        2: "two",
        3: "three",
        4: "four",
        5: "five",
        # Extend this as needed
    }
    length = len(input_string)
    return num_to_words.get(length, "unknown")
```

Now, let's conduct a couple of more tests to validate the description.

COMMAND: PYTHON(./temp/function.py example longer_string short)