From under- + trick.
undertrick (plural undertricks)
- (bridge) A trick that declarer does not win, causing the contract to go down.
2007 February 22, Phillip Alder, “Strong Spade Suit Helps Decide a Hard-Fought Match in Japan”, in New York Times[1]:Then the Netherlands scored an additional 3 imps for one fewer undertrick in a vulnerable one no-trump.