The Collaborative International Dictionary of English v.0.48:

Tegument \Teg"u*ment\, n. [L. tegumentum, from tegere to cover.
   See Thatch, n., and cf. Detect, Protect.]
   1. A cover or covering; an integument.
      [1913 Webster]

   2. Especially, the covering of a living body, or of some part
      or organ of such a body; skin; hide.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tegument
    n 1: a natural protective body covering and site of the sense of
         touch; "your skin is the largest organ of your body" [syn:
         skin, tegument, cutis]