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.
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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.
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         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.
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   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.
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   4. A frame of woodwork across a beach to accumulate and
      retain shingle. [Eng.] --Weale.
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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.
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         The hand that rounded Peter's dome,
         And groined the aisles of Christian Rome,
         Wrought in a sad sincerity.              --Emerson.
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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"