The Collaborative International Dictionary of English v.0.48:

Coexisting \Co`ex*ist"ing\, a.
   Coexistent. --Locke.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Coexist \Co`ex*ist\, v. i. [imp. & p. p. Coexisted; p. pr. &
   vb. n. Coexisting.]
   To exist at the same time; -- sometimes followed by with.
   [1913 Webster]

         Of substances no one has any clear idea, farther than
         of certain simple ideas coexisting together. --Locke.
   [1913 Webster]

         So much purity and integrity . . . coexisting with so
         much decay and so many infirmities.      --Warburton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

coexisting
    adj 1: existing at the same time [syn: coexistent,
           coexisting]