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"official proving of a will," c.1400, from Latin probatum "a thing proved," neuter of probatus "tried, tested, proved," past participle of probare "to try, test, prove" (see prove).
1560s, "to prove," from probate (n.) or from Latin probatus, past participle of probare. Specific sense of "prove the genuineness of a will" is from 1792. Related: Probated; probating.