The Collaborative International Dictionary of English v.0.48:

Coincide \Co`in*cide"\, v. i. [imp. & p. p. Coincided; p. pr.
   & vb. n. Coinciding.] [L. co- + incidere to fall on; in +
   cadere to fall: cf. F. co["i]ncider. See Chance, n.]
   1. To occupy the same place in space, as two equal triangles,
      when placed one on the other.
      [1913 Webster]

            If the equator and the ecliptic had coincided, it
            would have rendered the annual revoluton of the
            earth useless.                        --Cheyne.
      [1913 Webster]

   2. To occur at the same time; to be contemporaneous; as, the
      fall of Granada coincided with the discovery of America.
      [1913 Webster]

   3. To correspond exactly; to agree; to concur; as, our aims
      coincide.
      [1913 Webster]

            The rules of right jugdment and of good
            ratiocination often coincide with each other.
                                                  --Watts.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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