Source : Webster's Revised Unabridged Dictionary (1913)

Precondition \Pre`con*di"tion\, n.
   A previous or antecedent condition; a preliminary condition.

Source : WordNet®

precondition
     n 1: an assumption on which rests the validity or effect of
          something else [syn: {condition}, {stipulation}]
     2: an assumption that is taken for granted [syn: {given}, {presumption}]
     3: a condition that is a prerequisite
     v : put into the required condition beforehand