Webster's English Dictionary

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protein

pro.tein \'pro--.te-n, 'pro-t-e--*n\ n [F prote`ine, fr. LGk pro-teios 
   primary, fr. Gk pro-tos often attrib X first - more at PROT- 1: any of 
   numerous naturally occurring extremely complex combinations of am ino acids 
   that contain the elements carbon, hydrogen, nitrogen, oxygen, usu. sulfur, 
   occas. phosphorus, iron, or other elements, are essential constituents of 
   all living cells, and are synthesized from raw materials by plants but 
   assimilated as separate amino acids by animals 2: the total nitrogenous 
   material in plant or animal substances