Definition of "underbelly"

The soft underbelly of the dragon. In the legend, the dragon's armor doesn't cover its stomach.

1952 September, Philip K[indred] Dick, “The Gun”, in Planet Stories, New York, N.Y.: Love Romances Publishing Company; republished as The Collected Stories of Philip K. Dick, volume 1 (Beyond Lies the Wub), Los Angeles, Calif.: Underwood–Miller, 1987,

The biologist and his team were greeted by a nonstop squid review, with Humboldt squid darting in toward the boat and flashing their underbellies in attempts to lure small schooling fish near the surface.

2015, Michael Tennesen, The Next Species: The Future of Evolution in the Aftermath of Man, New York, N.Y.: Simon & Schuster; trade paperback edition, New York, N.Y.: Simon & Schuster Paperbacks, 2016 March, page 120

A jolt told me that the Nautilus had bumped the underbelly of the Ice Bank, still quite thick to judge from the hollowness of the accompanying noise.

1993, Jules Verne, chapter 37, in Walter James Miller, Frederick Paul Walter, transl., Jules Verne’s Twenty Thousand Leagues under the Sea: The Definitive Unabridged Edition Based on the Original French Texts, Annapolis, Md.: Naval Institute Press

In order to take the initiative, military leaders from Great Britain and the United States decided to attack in Africa, cross the Mediterranean, and move up against the "soft underbelly" of German-dominated Europe.

1967, Boyd C. Shafer, Richard A. McLemore, Everett Auspurger, Kenneth E. Miller, “World Cataclysm and the United States”, in Manual, Test, and Answers for 1865 to the Present: A United States History for High Schools, teachers’ edition, River Forest, Ill.: Laidlaw Brothers, page 98, column 2

The documents in this report reveal how such doctrinal disagreements have historically driven wedges within the upper echelons of al-Qa'ida. It is this intra-movement contention that comprises the soft underbelly of violent jihad, which can be exploited to great ends.

2006 February 14, “Organizational Vulnerabilities and Recommendations to Exploit Them”, in Harmony and Disharmony: Exploiting al-Qa’ida’s Organizational Vulnerabilities, [West Point, N.Y.]: Combating Terrorism Center, Department of Social Sciences, United States Military Academy, page 53

Twenty-one years after the movie "Trainspotting" gave the world a glimpse into Edinburgh's seedy, heroin-filled underbelly, the franchise is back on the map with “T2 Trainspotting.”

2017 January 26, Christopher D. Shea, “‘T2 Trainspotting’: The Early Reviews”, in The New York Times‎, archived from the original on 22 February 2017

The book arrives at a moment of reckoning for the running world, as more female runners have come forward to share their stories of the sport’s dark underbelly, one that can be rife with manipulation, eating disorders and physical and emotional abuse.

2023 March 25, Talya Minsberg, “In Her New Book, Kara Goucher Keeps Running Accountable”, in The New York Times‎