1. (a.) Consisting of four; by fours, or in sets of four.

2. (a.) Later than, or subsequent to, the Tertiary; Post-tertiary; as, the Quaternary age, or Age of man.

3. (n.) The number four.

4. (n.) The Quaternary age, era, or formation.

Little Joe biquadrate biquadratic four four-legged four-part diaphony four-rayed foursome foursquare quad quadrangle quadrature quadrennium quadric quadrilateral quadrille quadrinomial quadrivalent quadruped quadruplet quartet quartic quartile quatern quaternion quaternity quatrefoil rectangle square square dance squaring tetractinal tetrad tetragon tetragram tetragrammaton tetrahedron tetralogy tetraphony tetrapody tetravalent