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Webster 1913 Edition

Adj.

Like mutton; having a flavor of mutton.

muttony ‎(comparative more muttony, superlative most muttony)

Like mutton; having a flavour of mutton.
- 1891, Outing: Sport, Adventure, Travel, Fiction (volume 17, page 137)
  I confess to having felt a prejudice against sleeping in a bag, more especially a sheepskin bag, which would probably have a muttony odor; but it was pronounced to be the warmest and least cumbersome form of bedding we could have […]