Isaac Taylor thinks this phrase means toper's words, and derives fustian from fuste, Old French for a cask, whence “fusty” (tasting of the cask). It may be so, but we have numerous phrases derived from materials of dress applied to speech, as velvet, satin, silken, etc. The mother of Artaxerxes said, “Those who address kings must use silken words.” In French, “faire patte de velour ” means to fatten with velvet words in order to seduce or win over.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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