The Collaborative International Dictionary of English v.0.48:

Plat \Plat\, n. [Cf. Plat flat, which perh. caused this
   spelling, and Plot a piece of ground.]
   A small piece or plot of ground laid out with some design, or
   for a special use; usually, a portion of flat, even ground.
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         This flowery plat, the sweet recess of Eve. --Milton.
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         I keep smooth plat of fruitful ground.   --Tennyson.
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The Collaborative International Dictionary of English v.0.48:

Plat \Plat\, v. t.
   To lay out in plats or plots, as ground.
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The Collaborative International Dictionary of English v.0.48:

Plat \Plat\, a. [F. plat. See Plate, n.]
   Plain; flat; level. [Obs.] --Gower.
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The Collaborative International Dictionary of English v.0.48:

Plat \Plat\, adv.
   1. Plainly; flatly; downright. [Obs.]
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            But, sir, ye lie, I tell you plat.    --Rom. of R.
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   2. Flatly; smoothly; evenly. [Obs.] --Drant.
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The Collaborative International Dictionary of English v.0.48:

Plat \Plat\, n.
   1. The flat or broad side of a sword. [Obs. or Prov. Eng.]
      --Chaucer.
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   2. A plot; a plan; a design; a diagram; a map; a chart. [Obs.
      or Prov. Eng.] "To note all the islands, and to set them
      down in plat." --Hakluyt.
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The Collaborative International Dictionary of English v.0.48:

Plat \Plat\, v. t. [imp. & p. p. Platted; p. pr. & vb. n.
   Platting.] [See Plait.]
   To form by interlaying interweaving; to braid; to plait.
   "They had platted a crown of thorns." --Matt. xxvii. 29.
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The Collaborative International Dictionary of English v.0.48:

Plat \Plat\, n.
   Work done by platting or braiding; a plait.
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         Her hair, nor loose, nor tied in formal plat. --Shak.
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WordNet (r) 3.0 (2006):

plat
    n 1: a map showing planned or actual features of an area
         (streets and building lots etc.)
    v 1: make a plat of; "Plat the town" [syn: plat, plot]

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "plat":
   accordion pleat, acres, block, box pleat, chattels real, clearing,
   clos, close, corn field, crease, crimp, crisp, croft,
   cultivated land, demesne, dog-ear, domain, double, double over,
   enclave, enfold, field, flounce, flute, fold, fold over, forty,
   frill, gather, grounds, hayfield, honor, infold, interfold,
   knife pleat, kraal, land, landed property, lands, lap over, lot,
   lots, manor, messuage, paddy, pale, parcel, parcel of land, patch,
   piece of land, plait, pleat, plicate, plot, plot of ground, ply,
   praedium, property, quad, quadrangle, quadrat, quill, real estate,
   real property, realty, rice paddy, ruff, ruffle, section, square,
   tenements, toft, tract, tuck, turn over, twill, wheat field



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PLAT. A map of a piece of land, in which are marked the courses and
distances of the different lines, and the quantity of land it contains.
     2. Such a plat;nay be given in evidence in ascertaining the position of
the land, and what is included, and may serve to settle the figure of a
survey, and correct mistakes. 5 Monr. 160. See 17 Mass. 211; 5 Greenl. 219;
7 Greenl, 61; 4 Wheat. 444; 14 Mass. 149.