(Gr. hairesis, usually rendered "heresy", Acts 24:14; 1 Chr. 11:19; Gal. 5:20, etc.), meaning properly "a choice," then "a chosen manner of life," and then "a religious party," as the "sect" of the Sadducees (Acts 5:17), of the Pharisees (15:5), the Nazarenes, i.e., Christians (24:5). It afterwards came to be used in a bad sense, of those holding pernicious error, divergent forms of belief (2 Pet. 2:1; Gal. 5:20).
Easton's Bible Dictionary. M.G. Easton. 1897.