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.

Groin \Groin\, n. [F. groin, fr. grogner to grunt, L. grunnire.]
   The snout of a swine. [Obs.] --Chaucer.

Groin \Groin\, v. i. [F. grogner to grunt, grumble.]
   To grunt to growl; to snarl; to murmur. [Obs.] --Chaucer.

         Bears that groined coatinually.          --Spenser.

Groin \Groin\, n. [Icel. grein distinction, division, branch;
   akin to Sw. gren, branch, space between the legs, Icel.
   greina to distinguish, divide, Sw. grena to branch, straddle.
   Cf. {Grain} a branch.]
   1. (Anat.) The line between the lower part of the abdomen and
      the thigh, or the region of this line; the inguen.

   2. (Arch.) The projecting solid angle formed by the meeting
      of two vaults, growing more obtuse as it approaches the
      summit.

   3. (Math.) The surface formed by two such vaults.

   4. A frame of woodwork across a beach to accumulate and
      retain shingle. [Eng.] --Weale.

Source : WordNet®

groin
     n 1: the crease at the junction of the inner part of the thigh
          with the trunk together with the adjacent region and
          often including the external genitals [syn: {inguen}]
     2: a protective structure of stone or concrete; extends from
        shore into the water to prevent a beach from washing away
        [syn: {breakwater}, {groyne}, {mole}, {bulwark}, {seawall},
         {jetty}]
     v : build with groins; "The ceiling was groined"