The Collaborative International Dictionary of English v.0.48:

Synchondrosis \Syn`chon*dro"sis\, n.; pl. Synchondroses. [NL.,
   fr. Gr. ?; sy`n with + ? cartilage.] (Anat.)
   An immovable articulation in which the union is formed by
   cartilage. -- Syn`chon*dro"si*al, a.
   [1913 Webster]