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Webster 1913 Edition

Noun.

[L.

grassatio

, from grassari to go about.]

A wandering about with evil intentions; a rioting.

[Obs. & R.]

Feltham.

Noun.

[L. grassatio.] A wandering about. [Little used.]

grassation ‎(uncountable)

(obsolete, rare) A wandering about with evil intentions; a rioting.
(Can we find and add a quotation of Feltham to this entry?)