Where can we find a definitive meaning for the term 'creationism'?

Though a seemingly new or unfamiliar term, there are actually many lexical and technical definitions of creationism.

 It can be found in many well known dictionaries, for example in:

-Macmillan-  “The belief that the universe was created exactly as the Bible describes it.” 

-Merriam-Webster-  “A doctrine or theory holding that matter, the various forms of life, and the world were created by God out of nothing and usually in the way described in Genesis.”  

-Oxford-  “The belief that the universe and living organisms originate from specific acts of divine creation, as in the biblical account, rather than by natural processes such as evolution.”  

-American Heritage- “Belief in the supernatural origin of the universe or of humans and other living things, especially as based on the literal interpretation of the account of the creation related in the Bible.”