Source : Webster's Revised Unabridged Dictionary (1913)

Hosanna \Ho*san"na\ (h[-o]*z[a^]n"n[.a]), n.; pl. {Hosannas}
   (-n[.a]z). [Gr. ?, fr. Heb. h[=o]sh[=i]'[=a]h nn[=a]save now,
   save, we pray, h[=o]sh[=i]a' to save (Hiphil, a causative
   form, of y[=a]sha') + n[=a], a particle.]
   A Hebrew exclamation of praise to the Lord, or an invocation
   of blessings. ``Hosanna to the Highest.'' --Milton.

         Hosanna to the Son of David.             --Matt. xxi.
                                                  9.

Source : WordNet®

hosanna
     n : a cry of praise or adoration (to God)