(historical) In Ancient Rome, a public informer who received a fourth part.

plural of quadruplicity

A group of four things.

quadruplication

plural of quadruplator

(basketball) The achievement of a two-digit number of any four of points scored, assists, rebounds, blocks, or steals in a single game.

(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.)

a screw or worm gear having four equal threads and thus capable of being started in four places

(nautical) A light, narrow rowing boat, especially one used in competitive rowing, in which a four rowers each have two oars / (rowing, especially in plural) A race in which such craft participate

The next bluff in sequence after a double bluff and a triple bluff