coincidental

from WordNet (r) 3.0 (2006)

coincidental
    adj 1: occurring or operating at the same time; "a series of
           coincident events" [syn: {coincident}, {coincidental},
           {coinciding}, {concurrent}, {co-occurrent},
           {cooccurring}, {simultaneous}]

from The Collaborative International Dictionary of English v.0.48

Coincidental \Co*in`ci*den"tal\, a.
   Coincident.
   [1913 Webster]