The Collaborative International Dictionary of English v.0.48:

Protein \Pro"te*in\, n. (Physiol. Chem.)
   In chemical analysis, the total nitrogenous material in
   vegetable or animal substances, obtained by multiplying the
   total nitrogen found by a factor, usually 6.25, assuming most
   proteids to contain approximately 16 per cent of nitrogen.
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Proteid \Pro"te*id\, n. [Gr. prw^tos first.] (Physiol. Chem.)
   An older, imprecise term replaced by protein.

   Note: Proteid was defined in the 1913 Webster as "One of a
         class of amorphous nitrogenous principles, containing,
         as a rule, a small amount of sulphur; an albuminoid, as
         blood fibrin, casein of milk, etc. Proteids are present
         in nearly all animal fluids and make up the greater
         part of animal tissues and organs. They are also
         important constituents of vegetable tissues. See 2d
         Note under Food." -- Pro"te*id, a.

   Syn: protein.
        [1913 Webster +PJC]

   Defensive proteid (Physiol. Chem.), one of a class of
      proteid substances, present in some animal tissues and
      fluids, that make the body immune to certain infectious
      diseases by destroying or rendering inactive the toxic
      products of bacterial growth; -- this is an older term
      replaced by more precise modern immunological concepts
      such as antibody and immunoglobulin. [archaic]
      [Webster 1913 Suppl. +PJC]

The Collaborative International Dictionary of English v.0.48:

Protein \Pro"te*in\, n. [Gr. prw^tos first: cf. prwtei^on the
   first place.] (Physiol. Chem.)
   any polymer of an amino acid joined by peptide (amide) bonds.
   Most natural proteins have alpha-amino acids as the monomeric
   constituents. All classical enzymes are composed of protein,
   and control most of the biochemical transformations carrie
   dout in living cells. They may be soluble, as casein,
   albumins, and other globular proteins, or insoluble (e. g.
   "structural proteins"), as collagen or keratin. "albumin", an
   older term for protein, is now used primarily to refer to
   certain specific soluble globular proteins found in eggs or
   blood serum, e.g. bovine serum albumin, the main soluble
   protein in teh serum of cattle, used as an enzymatically
   inert protein in biochemical research.

   Note: In the 1913 dictionary, protein was defined as: "A body
         now known as alkali albumin, but originally considered
         to be the basis of all albuminous substances, whence
         its name."
         [1913 Webster + PJC]

   Protein crystal. (Bot.) See Crystalloid, n., 2.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

macromolecule \mac`ro*mol"e*cule\, n. (Chem., Biochem.)
   A very large molecule, especially a polymer having from
   hundreds to many thousands of atoms, such as DNA, RNA,
   protein, polysaccharide, polyethylene, polycarbonate,
   etc.
   [PJC]

WordNet (r) 3.0 (2006):

protein
    n 1: any of a large group of nitrogenous organic compounds that
         are essential constituents of living cells; consist of
         polymers of amino acids; essential in the diet of animals
         for growth and for repair of tissues; can be obtained from
         meat and eggs and milk and legumes; "a diet high in
         protein"

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "protein":
   albumin, albuminoid, amino acid, androcyte, antheridium,
   antherozoid, casein, chlorophyll, chromoprotein, collagen,
   dipeptide, edestin, elastin, fibroin, globin, globulin, glutenin,
   glycoprotein, hemoglobin, histone, ichthulin, interferon,
   lactalbumin, lecithoprotein, lipid, lipoprotein, lysozyme,
   male gamete, milt, mucin, nucleohistone, nucleoprotein, oryzenin,
   osseomucoid, peptide, peptone, phosphoaminolipide, phosphoprotein,
   pollen, prolamine, protamine, proteid, proteose, protide, salmine,
   scum, seed, semen, seminal fluid, serum globulin, sperm,
   sperm cell, spermagonium, spermatic fluid, spermatid,
   spermatiophore, spermatium, spermatocyte, spermatogonium,
   spermatophore, spermatozoa, spermatozoid, spermatozoon, tendomucin,
   thymus histone, zein