  We show that bipartite entanglements involving non-orthogonal states are {\it
necessarily nonmaximally} entangled, however {\it small} the non-orthogonality
may be. How the deviation from maximal entanglement is related to
nonorthogonality is quantified by using two independent measures of
entanglement corresponding to the violation of Bell's inequality and the
entropy measure respectively. This result is true even if one of the subsystems
has orthogonal states. An application of this is that a maximal violation of
Bell's inequality in entangled neutral kaons is not possible in the presence of
CP violation.
