The Collaborative International Dictionary of English v.0.48:

Illegitimate \Il`le*git"i*mate\, v. t. [imp. & p. p.
   Illegitimated; p. pr. & vb. n. Illegitimating.]
   To render illegitimate; to declare or prove to be born out of
   wedlock; to bastardize; to illegitimatize.
   [1913 Webster]

         The marriage should only be dissolved for the future,
         without illegitimating the issue.        --Bp. Burnet.
   [1913 Webster]