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1560s, devest (modern spelling is c.1600), from Middle French devester "strip of possessions," from Old French desvestir, from des- "away" (see dis-) + vestir "to clothe" (see vest (v.)).
The figurative sense of "strip of possessions" is earliest in English; reflexive sense of "to strip oneself of" is from c.1600. Economic sense (implied in divestment) is from 1955. Related: Divested; divesting.