di·ar·thro·sis 
(dī′är-thrōsĭs)
(dī′är-thrōsĭs)n. pl. di·ar·thro·ses (-sēz)
Any of several types of bone articulation permitting free motion in a joint, as that of the shoulder or hip.
[Greek diarthrōsis, from diarthroun, to articulate : dia-, between; see DIA- + arthroun, to fasten by a joint (from arthron, joint; see ar- in the Appendix of Indo-European roots).]
di′ar·throdi·al (-dē-əl) adj.