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.
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 - vincx + y.
3. (Anat.) A band or bundle of fibers; a fraenum.
4. (Zool.) A commissure uniting the two main tendons in the
foot of certain birds.