A rare and tightly controlled substance required to build an isolytic weapon, sought by Cleveland Booker and Ruon Tarka in 3190 for their plan to destroy the Dark Matter Anomaly.
Isolynium is a scarce material whose trade is restricted because of its use in isolytic weapons, which are banned for the lasting damage they do to subspace.
It appears in the fourth-season Discovery episode All In. Having broken with the Federation over how to deal with the anomaly, Book and the scientist Ruon Tarka travel to the Karma Barge, a gambling den run by the broker Haz Mazaro, who has a supply for sale. Michael Burnham and Joann Owosekun arrive with orders to stop them obtaining it.
Mazaro sets the two sides to compete for the prize, ending in a card game that Book wins. With the isolynium Tarka completes his weapon, which is used against the anomaly's controller in the episodes that follow.