Vinculum

Part of speech: noun (n.)

1. A bond of union; a tie.

2. 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 x2 + y2 - x + y.

3. A band or bundle of fibers; a frænum.

4. A commissure uniting the two main tendons in the foot of certain birds.