Q.E.D.

Origin of Q.E.D.

First recorded in 1810–20, Q.E.D. is from the Latin word quod erat dēmōnstrandum
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Word Origin and History for q.e.d.

Q.E.D.

1760, abbreviation of Latin quod erat demonstrandum "which was to be demonstrated."

Online Etymology Dictionary, © 2010 Douglas Harper