I just read this helpful definition of scientism (think Richard Dawkins, et. al.) by John Polkinghorne:
“Scientism is the metaphysical belief that science tells us all that can be known or is worth knowing. It must clearly be distinguished from science itself which, owing to its intrinsic limitation to only a certain kind of encounter with reality, is far from being in a position to make such an overblown claim for its explanatory power. Science has bracketed out too much (meaning, purpose, beauty) from its consideration for it to be the universal source of understanding.”
– John Polkinghorne, Science and Religion in Quest of Truth (New Haven: Yale University Press, 2011), p. 23.