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Webster 1828 Edition

Adj.

Using language scurrilous, opprobrious, obscene or profane; uttering abuse, or profane or obscene words; accustomed to use bad language.

So foulmouthed a witness never appeared in any cause.

See also: foul-mouthed

foulmouthed ‎(comparative more foulmouthed, superlative most foulmouthed)