Entry 1 sense Webster, 1913 Hypergol /(hī"pẽr*gŏ)/ · Hy·per·gol · IPA 01 a. A substance which can form one of a pair of hypergolic substances. See hypergolic. 1. A substance which can form one of a pair of hypergolic substances. See hypergolic.(Rocketry) See: hypergolic