[billnotgatez]

I have been on this forum for eons and never noticed the words "perfect gas law".
Fortunately for me WIKI says it is synonymous with "ideal gas law".
What a space cadet am I!

[Arkcon]

Can't recall if they called it the perfect gas law when I was in high school.  Maybe they did, or maybe I read it in a much older book.  What does Paulings' Chemistry call it, especially in very old revisions?  That would definitively let us know if it was an older construction of the term.

[Borek]

In Polish we call them "gazy doskonałe" - "doskonały" can be translated as perfect, ideal, supreme and so on (compare https://ling.pl/slownik/polsko-angielski/doskonały ). My bet is "perfect" started as a poor translation (not necessarily from Polish).

[Enthalpy]

Translation from French.

[Arkcon]

Chemistry, Pauling and Pauling, (c) 1975, pp 103 -- The Complete Perfect-gas Equation.  So that's another reference.