From BiblePortal Wikipedia

Webster's Dictionary [1]

(1): ( n.) Specif., the principles and characteristics professed or represented by a 19th-century school of realistic writers, notably by Zola and Maupassant, who aimed to give a literal transcription of reality, and laid special stress on the analytic study of character, and on the scientific and experimental nature of their observation of life.

(2): ( n.) The theory that art or literature should conform to nature; realism; also, the quality, rendering, or expression of art or literature executed according to this theory.

(3): ( n.) The doctrine of those who deny a supernatural agency in the miracles and revelations recorded in the Bible, and in spiritual influences; also, any system of philosophy which refers the phenomena of nature to a blind force or forces acting necessarily or according to fixed laws, excluding origination or direction by one intelligent will.

(4): ( n.) A state of nature; conformity to nature.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [2]

is the name given to those systems of the philosophy of nature which explain the phenomnena by a blind force acting necessarily. This doctrine is to be found in Lucretius, and was held by Leucippus and Epicurus. The Systfee de la Nature of D'Holbach, the Traite de la Nature of Robinet, and the Philosophie de la Nature of Delisle de Sales, also contain it. In theology the term naturalism is applied to all those forms of belief or speculation which deny the doctrine of a personal God as the author and governor of the universe; being thus opposed to Theism (q.v.). See Literature appended to article (See Natural Theology).

The Nuttall Encyclopedia [3]

A philosophical term used to denote the resolution of the supernatural into the natural, and its obliteration; the reference of everything to merely natural laws, and the denial of all supernatural interference with them.