Source : Webster's Revised Unabridged Dictionary (1913)

Lanugo \La*nu"go\, n. [See {Lanuginose}.] (Anat.)
   The soft woolly hair which covers most parts of the mammal
   fetus, and in man is shed before or soon after birth.

Source : WordNet®

lanugo
     n : the fine downy hair covering a human fetus; normally shed
         during the ninth month of gestation