The Collaborative International Dictionary of English v.0.48:

Diazeuctic \Di`a*zeuc"tic\, Diazeutic \Di`a*zeu"tic\, a. [Gr. ?
   disjunctive, fr. ? to disjoin; dia` through, asunder + ? to
   join, yoke.] (Anc. Mus.)
   Disjoining two fourths; as, the diazeutic tone, which, like
   that from F to G in modern music, lay between two fourths,
   and, being joined to either, made a fifth. [Obs.]
   [1913 Webster]