vinculum

from The Collaborative International Dictionary of English v.0.48
Vinculum \Vin"cu*lum\, n.; pl. L. {Vincula}, E. {Vinculums}.
   [L., from vincire, vinctum, to bind.]
   1. A bond of union; a tie.
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   2. (Math.) A straight, horizontal mark placed over two or
      more members of a compound quantity, which are to be
      subjected to the same operation, as in the expression
      x^{2} + y^{2} - vinc{x + y}.
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   3. (Anat.) A band or bundle of fibers; a fraenum.
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   4. (Zool.) A commissure uniting the two main tendons in the
      foot of certain birds.
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