NOUN (2)

1. a small crown; usually indicates a high rank but below that of sovereign;

2. margin between the skin of the pastern and the horn of the hoof;

The Collaborative International Dictionary of English v.0.48:

Coronet \Cor"o*net\ (k?r"?-n?t), n. [Dim. of OE. corone crown;
   cf. OF. coronete. See Crown, and cf. Crownet, Cronet.]
   [1913 Webster]
   1. An ornamental or honorary headdress, having the shape and
      character of a crown; particularly, a crown worn as the
      mark of high rank lower than sovereignty. The word is used
      by Shakespeare to denote also a kingly crown.
      [1913 Webster]

            Without a star, a coronet, or garter. --Goldsmith.
      [1913 Webster]

   Note: The coronet of the Prince of Wales consist of a circlet
         of gold with four crosses patt['e]e around the edge
         between as many fleurs-de-lis. The center crosses are
         connected by an arch which is surmounted by a globe or
         cross. The coronet of a British duke is adorned with
         strawberry leaves; that of a marquis has leaves with
         pearls interposed; that of an earl raises the pearls
         above the leaves; that of a viscount is surrounded with
         pearls only; that of a baron has only four pearls.
         [1913 Webster]

   2. (Far.) The upper part of a horse's hoof, where the horn
      terminates in skin. --James White.
      [1913 Webster]

   3. (Anc. Armor) The iron head of a tilting spear; a coronel.
      --Crose.
      [1913 Webster]

WordNet (r) 3.0 (2006):

coronet
    n 1: a small crown; usually indicates a high rank but below that
         of sovereign
    2: margin between the skin of the pastern and the horn of the
       hoof

Moby Thesaurus II by Grady Ward, 1.0:

183 Moby Thesaurus words for "coronet":
   O, achievement, alerion, animal charge, anklet, annular muscle,
   annulet, annulus, areola, argent, armlet, armorial bearings,
   armory, arms, aureole, azure, bandeau, bangle, bar, bar sinister,
   baton, beads, bearings, bend, bend sinister, bijou, billet, blazon,
   blazonry, bordure, bracelet, breastpin, broad arrow, brooch,
   cadency mark, canton, cap of dignity, cap of maintenance, chain,
   chaplet, charge, charm, chatelaine, chevron, chief, circle,
   circuit, circumference, circus, closed circle, coat of arms,
   cockatrice, corona, coronal, crescent, crest, cross, cross moline,
   crown, cycle, device, diadem, difference, differencing, discus,
   disk, eagle, earring, ermine, ermines, erminites, erminois,
   escutcheon, eternal return, fairy ring, falcon, fess, fess point,
   field, file, flanch, fleur-de-lis, fob, fret, fur, fusil, garland,
   gem, glory, great seal, griffin, gules, gyron, halo, hatchment,
   helmet, heraldic device, honor point, impalement, impaling,
   inescutcheon, jewel, label, lasso, lion, locket, logical circle,
   loop, looplet, lozenge, magic circle, mantling, marshaling,
   martlet, mascle, metal, motto, mullet, necklace, nombril point,
   noose, nose ring, octofoil, or, orb, orbit, ordinary, orle, pale,
   paly, pean, pheon, pin, precious stone, privy seal, purple,
   purple pall, purpure, quarter, quartering, radius, regalia,
   rhinestone, ring, robe of state, rod, rod of empire, rondelle,
   rose, round, roundel, royal crown, sable, saltire, saucer, scepter,
   scutcheon, seal, shield, signet, sphincter, spread eagle, stickpin,
   stone, subordinary, tenne, tiara, tincture, torque, torse,
   tressure, triple plume, unicorn, uraeus, vair, vert,
   vicious circle, wampum, wheel, wreath, wristband, wristlet, yale