power law vs law of nature

power law and law of nature both are nouns.

Word	Noun	Adjective	Verb	Adverb
power law	Yes	No	No	No
law of nature	Yes	No	No	No

As nouns, law of nature is a hypernym of power law; that is, law of nature is a word with a broader meaning than power law:

power law: (psychophysics) the concept that the magnitude of a subjective sensation increases proportional to a power of the stimulus intensity
law of nature: a generalization that describes recurring facts or events in nature

Other hypernyms of power law include law.

power law (noun)	law of nature (noun)
(psychophysics) the concept that the magnitude of a subjective sensation increases proportional to a power of the stimulus intensity	a generalization that describes recurring facts or events in nature