Scientism is, roughly speaking, the belief that the only legitimate knowledge is scientific knowledge and all other sources of knowledge - like religion - should be rejected.
If it is still unlcear, here is the relevant Wikipedia link: https://en.wikipedia.org/wiki/Scientism
Now in my language (Polish) there are two distinct terms: "naukowiec" - which means a scientist (the person who conducts scientific research and who can win a Nobel prize for discovering a vaccine against AIDS) and "scjentysta" - which means a person whose worldview is in accordance to scientism (so "scjentysta" will reject all arguments that are not scientific in nature and will condemn religion).
But, how to say "scjentysta" in English? Since what I want is a believer of scientism, I would say "scientist" BUT - this will cause confusion since not every practicioner of science believes in scientism and not every person whose worldview is in accordance with scientism will have PhD.
So, is my only option still "scientist" or is there any better word?
"A ___ believes that science is the only legitimate source of knowledge."
As opposed to:
"A scientist has won the Nobel prize for discovering a vaccine against AIDS."