Source : Webster's Revised Unabridged Dictionary (1913)

Disappearance \Dis`ap*pear"ance\, n.
   The act of disappearing; cessation of appearance; removal
   from sight; vanishing. --Addison.

Source : WordNet®

disappearance
     n 1: the act of leaving secretly or without explanation [syn: {disappearing}]
          [ant: {appearance}]
     2: the event of passing out of sight [ant: {appearance}]
     3: gradually ceasing to be visible [syn: {fade}]