Set Off Meaning

(printing, historical) To deface or soil the next sheet; said of the ink on a freshly printed sheet, when another sheet comes in contact with it before it has had time to dry.

Example:   He set off in search of better opportunities.
  I had no idea that one simple comment would set off such a huge argument.
  What a tragedy, that someone would set off a bomb in a crowded place.
  Don't set him off or he won't shut up all day.
  My taxes did not increase because the amount of my raise was set off by my losses in the stock market.
1881, Henry James, Jr., The Portrait of a Lady, Chapter XXXIX, in The Atlantic Monthly, Volume XLVIII, Number CCLXXXVI (August, 1881), Houghton, Mifflin, and Company, page 215:
  When a woman had made such a mistake, there was only one way to repair it,—to accept it. One folly was enough, especially it was to last for ever; a second one would not much set it off.