The Collaborative International Dictionary of English v.0.48:

Hosanna \Ho*san"na\ (h[-o]*z[a^]n"n[.a]), n.; pl. Hosannas
   (-n[.a]z). [Gr. ?, fr. Heb. h[=o]sh[imac]'[=a]h nn[=a]save
   now, save, we pray, h[=o]sh[imac]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.
   [1913 Webster]

         Hosanna to the Son of David.             --Matt. xxi.
                                                  9.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hosanna
    n 1: a cry of praise or adoration (to God)

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "hosanna":
   Agnus Dei, Benedicite, Gloria, Gloria Patri, Gloria in Excelsis,
   Introit, Magnificat, Miserere, Nunc Dimittis, Te Deum, Trisagion,
   Vedic hymn, alleluia, answer, anthem, antiphon, antiphony,
   applause, canticle, chant, cheer, chorale, chorus of cheers, cry,
   doxology, hallelujah, hooray, hurrah, hurray, huzzah, hymn,
   hymn of praise, hymnody, hymnography, hymnology, laud, mantra,
   motet, offertory, offertory sentence, paean, psalm, psalmody, rah,
   report, response, responsory, shout, versicle, yell, yippee



Easton's 1897 Bible Dictionary:

Hosanna
   Save now! or Save, we beseech, (Matt. 21:9). This was a
   customary form of acclamation at the feast of Tabernacles.
   (Comp. Ps. 118:25.)


Hitchcock's Bible Names Dictionary (late 1800's):

Hosanna, save I pray thee; keep; preserve