The Collaborative International Dictionary of English v.0.48:

Thin \Thin\, a. [Compar. Thiner; superl. Thinest.] [OE.
   thinne, thenne, thunne, AS. [thorn]ynne; akin to D. dun, G.
   d["u]nn, OHG. dunni, Icel. [thorn]unnr, Sw. tunn, Dan. tynd,
   Gael. & Ir. tana, W. teneu, L. tenuis, Gr. ? (in comp.)
   stretched out, ? stretched, stretched out, long, Skr. tanu
   thin, slender; also to AS. ?enian to extend, G. dehnen, Icel.
   ?enja, Goth. ?anjan (in comp.), L. tendere to stretch, tenere
   to hold, Gr. ? to stretch, Skr. tan. [root]51 & 237. Cf.
   Attenuate, Dance, Tempt, Tenable, Tend to move,
   Tenous, Thunder, Tone.]
   1. Having little thickness or extent from one surface to its
      opposite; as, a thin plate of metal; thin paper; a thin
      board; a thin covering.
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   2. Rare; not dense or thick; -- applied to fluids or soft
      mixtures; as, thin blood; thin broth; thin air. --Shak.
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            In the day, when the air is more thin. --Bacon.
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            Satan, bowing low
            His gray dissimulation, disappeared,
            Into thin air diffused.               --Milton.
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   3. Not close; not crowded; not filling the space; not having
      the individuals of which the thing is composed in a close
      or compact state; hence, not abundant; as, the trees of a
      forest are thin; the corn or grass is thin.
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            Ferrara is very large, but extremely thin of people.
                                                  --Addison.
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   4. Not full or well grown; wanting in plumpness.
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            Seven thin ears . . . blasted with the east wind.
                                                  --Gen. xli. 6.
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   5. Not stout; slim; slender; lean; gaunt; as, a person
      becomes thin by disease.
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   6. Wanting in body or volume; small; feeble; not full.
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            Thin, hollow sounds, and lamentable screams.
                                                  --Dryden.
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   7. Slight; small; slender; flimsy; wanting substance or depth
      or force; superficial; inadequate; not sufficient for a
      covering; as, a thin disguise.
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            My tale is done, for my wit is but thin. --Chaucer.
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   Note: Thin is used in the formation of compounds which are
         mostly self-explaining; as, thin-faced, thin-lipped,
         thin-peopled, thin-shelled, and the like.
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   Thin section. See under Section.
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