The function returns "one" if the input string contains the substring "abc", otherwise it returns "zero".
[CODE]:
```python
def f(x):
    if "abc" in x:
        return "one"
    else:
        return "zero"
```

Please note that this is just an approximation based on the given input-output pairs. It might not accurately capture all the behavior of the function, so further testing may be required to refine the description.