Source : Webster's Revised Unabridged Dictionary (1913)

Groin \Groin\, v. t. [imp. & p. p. {Groined}; p. pr. & vb. n.
   {Groining}.] (Arch.)
   To fashion into groins; to build with groins.

         The hand that rounded Peter's dome, And groined the
         aisles of Christian Rome, Wrought in a sad sincerity.
                                                  --Emerson.