Based on the experiments I ran, here is a description of the function implemented by f(x):

[DESCRIPTION]: The function f(x) assigns values between 0 and 1 to words, indicating the association of each word with a particular concept. From the experiments, it seems that f(x) is highly selective for the concept of "pen". Words like "pen" have a much higher output value (0.1192 in this case) compared to other words. Some other words like "table" (0.0040), "sun" (0.0015), and "fire" (0.0006) also have relatively higher output values, but they are not as highly associated with the concept as "pen".

It is important to note that this is just a preliminary description based on the experiments conducted so far. Further experimentation and analysis may be needed to fully understand the behavior of f(x) and determine if it is selective for any other concepts.