The Collaborative International Dictionary of English v.0.48:

Interdependence \In`ter*de*pend"ence\, n.
   Mutual dependence. "The interdependence of virtue and
   knowledge." --M. Arnold.
   [1913 Webster]

WordNet (r) 3.0 (2006):

interdependence
    n 1: a reciprocal relation between interdependent entities
         (objects or individuals or groups) [syn: mutuality,
         interdependence, interdependency]