Based on the tests I ran, it seems that the function is providing higher values (closer to 1) for words related to nature or natural objects (such as "tree" in this case) compared to words related to animals (such as "cat" and "dog") or objects related to man-made things (such as "car"). The function gives a relatively low value for the word "love". 

Therefore, a possible description of the function could be:

[DESCRIPTION]: The function f(x) seems to be selective for words related to nature or natural objects, providing higher values for those words compared to words related to animals or man-made objects. It also gives a relatively low value for the word "love".