The Collaborative International Dictionary of English v.0.48:

Quaternary \Qua*ter"na*ry\, n. [L. numerus quaternarius: cf. F.
   quaternaire.]
   1. The number four. --Boyle.
      [1913 Webster]

   2. (Geol.) The Quaternary age, era, or formation. See the
      Chart of Geology.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Quaternary \Qua*ter"na*ry\, a. [L. quaternarius consisting of
   four each, containing four, fr. quaterni four each, fr.
   quattuor four: cf. F. quaternaire. See Four.]
   [1913 Webster]
   1. Consisting of four; by fours, or in sets of four.
      [1913 Webster]

   2. (Geol.) Later than, or subsequent to, the Tertiary;
      Post-tertiary; as, the Quaternary age, or Age of man.
      [1913 Webster]

WordNet (r) 3.0 (2006):

quaternary
    adj 1: consisting of or especially arranged in sets of four;
           "quaternate leaves"; "a quaternary compound" [syn:
           quaternate, quaternary]
    2: coming next after the third and just before the fifth in
       position or time or degree or magnitude; "the quaternary
       period of geologic time extends from the end of the tertiary
       period to the present" [syn: fourth, 4th, quaternary]
    n 1: last 2 million years [syn: Quaternary, Quaternary
         period, Age of Man]
    2: the cardinal number that is the sum of three and one [syn:
       four, 4, IV, tetrad, quatern, quaternion,
       quaternary, quaternity, quartet, quadruplet,
       foursome, Little Joe]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "quaternary":
   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