SAINT, n. A dead sinner, revised and edited.

Ambrose Bierce (1842-1914?) American writer and journalist

“Saint,” The Devil’s Dictionary (1911)
    (Source)

Originally published in The Devil's Dictionary [A-Z] as Vol. 7 of his Collected Works.

This seems to have been a revision of:

CANONIZE, v.t.. To make a saint out of a dead sinner.
 

That entry first appeared in the "Devil's Dictionary" column in the San Francisco Wasp (1881-06-11), but was never collected in book form.