late 14c., champertie, champartie, the illegal act whereby a person not otherwise interested makes a bargain to maintain a litigant in return for a share of the property in dispute if the case succeeds, from Old French champart "portion of produce received by a feudal lord from land held in lease from him" (13c.), from Medieval Latin campipartem, from campi pars "part of the field" (see campus + part (n.)).
word-forming element making adjectives from nouns, meaning "having, full of, having to do with, doing, inclined to," from Old French -ous, -eux, from Latin -osus (compare -ose (1)). In chemistry, "having a lower valence than forms expressed in -ic."
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Harper, D. (n.d.). Etymology of champertous. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/champertous