To assign a quantity to. / To determine the value of (a variable or expression).

(geometry) A geometric shape with four angles and four straight sides; a four-sided polygon. / A courtyard which is quadrangular. / The buildings forming the border of such a courtyard.

(education, historical) The higher division of the seven liberal arts in the Middle Ages, composed of geometry, astronomy, arithmetic, and music.

(quantum mechanics) A quantum field theory in particle physics which describes the strong interaction of quarks and gluons employing the concept of color charge.

Divided into four parts. / Involving four parties or participants; four-party.

A treatise divided into four parts.

(finance) Simultaneous expiry on US markets of stock index futures, stock index options, stock options, and single stock futures, which takes place on the third Friday of March, June, September, and December. (Prior to single stock futures those days were triple witching.)

(number theory) The mathematical theorem which states that, for given odd prime numbers p and q, the question of whether p is a square modulo q is equivalent to the question of whether q is a square modulo p.

(mathematics) A number (real or complex) which is a solution to an equation of the form x²+Bx+C=0 for some integers B and C. For example 42, or 2+3i, or 1+√/2.

(informal, idiomatic) To be very frightened, scared, or nervous.