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Webster 1913 Edition

Adj.

[See

Being in unison; unisonant.

Busby.

Adj.

Being in unison.

unisonous ‎(comparative more unisonous, superlative most unisonous)

Being in unison; unisonant.
- 1860, Lowell Mason, ‎Edwards Amasa Park, ‎Austin Phelps, The Sabbath hymn and tune book (page iii)
  Hitherto all the singing in the American churches had been unisonous, the melody only having been sung; but in 1720 a book of tunes in threo parts, "Cantus," "Medius" and "Basus," was published by Rev. Thomas Walter.

unisonant — see unisonant