The Collaborative International Dictionary of English v.0.48:

groin \groin\ (groin), n. [F. groin, fr. grogner to grunt, L.
   grunnire.]
   The snout of a swine. [Obs.] --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Groin \Groin\, v. i. [F. grogner to grunt, grumble.]
   To grunt to growl; to snarl; to murmur. [Obs.] --Chaucer.
   [1913 Webster]

         Bears that groined coatinually.          --Spenser.
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The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. (Arch.) The projecting solid angle formed by the meeting
      of two vaults, growing more obtuse as it approaches the
      summit.
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   3. (Math.) The surface formed by two such vaults.
      [1913 Webster]

   4. A frame of woodwork across a beach to accumulate and
      retain shingle. [Eng.] --Weale.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Groin \Groin\, v. t. [imp. & p. p. Groined (groind); p. pr. &
   vb. n. Groining.] (Arch.)
   To fashion into groins; to build with groins.
   [1913 Webster]

         The hand that rounded Peter's dome,
         And groined the aisles of Christian Rome,
         Wrought in a sad sincerity.              --Emerson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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: groin, inguen]
    2: a curved edge formed by two intersecting vaults
    3: a protective structure of stone or concrete; extends from
       shore into the water to prevent a beach from washing away
       [syn: breakwater, groin, groyne, mole, bulwark,
       seawall, jetty]
    v 1: build with groins; "The ceiling was groined"

Moby Thesaurus II by Grady Ward, 1.0:

104 Moby Thesaurus words for "groin":
   V, abutment, anchorage, anchorage ground, arc-boutant, arch dam,
   backstop, bamboo curtain, bank, bar, barrage, barrier, basin, beam,
   bear-trap dam, beaver dam, berth, boom, branch, breakwater,
   breastwork, brick wall, buffer, bulkhead, bulwark, buttress,
   buttress pier, buttressing, cofferdam, crotch, crutch, dam,
   defense, delta, dike, ditch, dock, dockage, dockyard, dry dock,
   earthwork, embankment, fan, fence, flying buttress, fork, furcula,
   furculum, gate, gravity dam, hanging buttress, harbor, harborage,
   haven, hydraulic-fill dam, inguen, iron curtain, jam, jetty, jutty,
   landing, landing place, landing stage, leaping weir, levee, logjam,
   marina, milldam, moat, mole, moorings, mound, offshoot, parapet,
   pier, pier buttress, port, portcullis, prong, protected anchorage,
   quay, ramification, rampart, retaining wall, road, roadblock,
   roads, roadstead, rock-fill dam, seaport, seawall, shipyard,
   shoulder, shutter dam, slip, stem, stone wall, trident, wall, weir,
   wharf, wicket dam, wishbone, work