Source : Webster's Revised Unabridged Dictionary (1913)

Overgrowth \O"ver*growth`\, n.
   Excessive growth.

Source : WordNet®

overgrowth
     n 1: excessive size; usually caused by excessive secretion of
          growth hormone from the pituitary gland [syn: {giantism},
           {gigantism}]
     2: a profusion of growth on or over something else