vinculum

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Mathematics A bar drawn over two or more algebraic terms to indicate that they are to be treated as a single term.
• noun Anatomy A bandlike structure, such as a ligament.
• noun A bond or tie.

from The Century Dictionary.

• noun A bond of union; a bond; a tie.
• noun In algebra, a character in the form of a stroke or brace drawn over a quantity when it consists of several terms, in order to connect them together as one quantity and show that they are to be multiplied or divided, etc., together: thus, , indicates that the sum of a and b is to be multiplied by c; whereas the expression without this character would indicate simply that b is to be multiplied by c, and the product added to adjective
• noun In printing, a brace.
• noun In anatomy, a tendinous or ligamentous band uniting certain parts; a frenum.

from the GNU version of the Collaborative International Dictionary of English.

• noun A bond of union; a tie.
• noun (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 x2 + y2 - x + y.
• noun (Anat.) A band or bundle of fibers; a frænum.
• noun (Zoöl.) A commissure uniting the two main tendons in the foot of certain birds.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A bond or link signifying union.
• noun arithmetic, obsolete Any symbol used to group some of the terms in an expression, indicating that that part of the calculation should be done before other parts.
• noun arithmetic A horizontal line over the top of some of the terms in an expression, indicating that that part of the calculation is to be done before other parts.
• noun Australia, arithmetic Specifically, the horizontal line between the numerator and denominator in a fraction.
• noun anatomy A ligament that limits the movement of an organ or part.