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Webster 1828 Edition

Adj.

s as z.

Not musical; not harmonious or melodious.

Harsh; not pleasing to the ear.

unmusical ‎(comparative more unmusical, superlative most unmusical)

Not musical: lacking in musical ability.
Not musical: unmelodic.
- 1870, The African Repository and Colonial Journal (volume 46, page 231)
  The harp itself was a huge gourd, and a most unmusical "shell" it proved to be.