(physics) A quantum number that specifies the spin of a particle; for an electron, it may only take the values ±1/2

(physics) The quantum number (of an atomic orbital) that specifies the energy of an electron in an atom and, hence, which shell it occupies

plural of sine qua non

A form of roller hockey played on four-wheeled roller skates.

A roller skate with four wheels, two either side of the foot.

(algebraic number theory) A number field that is an extension field of degree two over the rational numbers.

(medicine, usually plural only) Rough divisions of the abdominal cavity formed by placing the umbilicus at the center of the horizontal and vertical dividing lines.

quadrille paper

(quantum mechanics) A momentary fluctuation in the energy at a point in space due to the Heisenberg uncertainty principle

(physics) A normalized linear combination of an "up" state and a "down" state for, say, the spin of an electron.