I have tested a diverse range of words, and observed the function's output. Based on the input-output pairs, here's my description of the function f(x):

[DESCRIPTION]: The function f(x) assigns higher values to more obscure and specific words, especially those related to affinities for specific phenomena or objects (e.g., pluviophile, selenophile). The function generally outputs lower values for common and general words.

It is selective for concepts involving specific affinities/interests and obscure words.