The Collaborative International Dictionary of English v.0.48:

Slender \Slen"der\, a. [Compar. Slenderer; superl.
   Slenderest.] [OE. slendre, sclendre, fr. OD. slinder thin,
   slender, perhaps through a French form; cf. OD. slinderen,
   slidderen, to creep; perh. akin to E. slide.]
   1. Small or narrow in proportion to the length or the height;
      not thick; slim; as, a slender stem or stalk of a plant.
      "A slender, choleric man." --Chaucer.
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            She, as a veil down to the slender waist,
            Her unadorned golden tresses wore.    --Milton.
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   2. Weak; feeble; not strong; slight; as, slender hope; a
      slender constitution.
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            Mighty hearts are held in slender chains. --Pope.
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            They have inferred much from slender premises. --J.
                                                  H. Newman.
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            The slender utterance of the consonants. --J. Byrne.
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   3. Moderate; trivial; inconsiderable; slight; as, a man of
      slender intelligence.
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            A slender degree of patience will enable him to
            enjoy both the humor and the pathos.  --Sir W.
                                                  Scott.
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   4. Small; inadequate; meager; pitiful; as, slender means of
      support; a slender pittance.
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            Frequent begging makes slender alms.  --Fuller.
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   5. Spare; abstemious; frugal; as, a slender diet.
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            The good Ostorius often deigned
            To grace my slender table with his presence.
                                                  --Philips.
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   6. (Phon.) Uttered with a thin tone; -- the opposite of
      broad; as, the slender vowels long e and i.
      [1913 Webster] -- Slen"der*ly, adv. -- Slen"der*ness,
      n.
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WordNet (r) 3.0 (2006):

slenderness
    n 1: the quality of being slight or inadequate; "he knew the
         slenderness of my wallet"; "the slenderness of the chances
         that anything would be done"; "the slenderness of the
         evidence"
    2: relatively small dimension through an object as opposed to
       its length or width; "the tenuity of a hair"; "the thinness
       of a rope" [syn: thinness, tenuity, slenderness] [ant:
       thickness]
    3: the property of an attractively thin person [syn:
       slenderness, slightness, slimness]