The Collaborative International Dictionary of English v.0.48:

Tenuity \Te*nu"i*ty\, n. [L. tenuitas, from tenuis thin: cf. F.
   t['e]nuit['e]. See Tenuous.]
   1. The quality or state of being tenuous; thinness, applied
      to a broad substance; slenderness, applied to anything
      that is long; as, the tenuity of a leaf; the tenuity of a
      hair.
      [1913 Webster]

   2. Rarily; rareness; thinness, as of a fluid; as, the tenuity
      of the air; the tenuity of the blood. --Bacon.
      [1913 Webster]

   3. Poverty; indigence. [Obs.] --Eikon Basilike.
      [1913 Webster]

   4. Refinement; delicacy.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tenuity
    n 1: 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]
    2: a rarified quality; "the tenuity of the upper atmosphere"
       [syn: rarity, tenuity, low density]
    3: the quality of lacking intensity or substance; "a shrill yet
       sweet tenuity of voice"- Nathaniel Hawthorne [syn:
       feebleness, tenuity]