Source : Webster's Revised Unabridged Dictionary (1913)

Diarthrosis \Di`ar*thro"sis\, n. [NL., fr. Gr. ?, fr. ? to
   joint, articulate; dia` through, asunder + ? to fasten by a
   joint, 'a`rqron joint.] (Anat.)
   A form of articulation which admits of considerable motion; a
   complete joint; abarticulation. See {Articulation}.

Source : WordNet®

diarthrosis
     n : a joint so articulated as to move freely [syn: {synovial
         joint}, {articulatio synovialis}]
     [also: {diarthroses} (pl)]